At present, metal/metal oxide composites are considered as potential oxygen reduction reaction (ORR) catalysts for energy-related applications like fuel cells. Here, we fabricated a high-activity, low Pt loading ORR electrocatalyst composed of nanoporous Pt (np-Pt) in intimate contact with lamellar (Mn,Al)3O4 nanosheet (NS). In comparison to Pt/C (Johnson Matthey), the np-Pt/(Mn,Al)3O4 NS catalyst shows a 11.5-fold enhancement in the mass-normalized ORR activity and much better methanol tolerance because of the metal–support interactions between np-Pt and (Mn,Al)3O4. Furthermore, the combination of electrochemical experiments with theoretical calculations verifies that the ORR on the np-Pt/(Mn,Al)3O4 NS catalyst is a direct 4e– pathway in the alkaline solution. In addition, the electrocatalytic mechanisms have also been rationalized by density functional theory (DFT) calculations.Keywords: density functional theory (DFT) calculations; methanol tolerance; nanoporous platinum; oxygen reduction reaction (ORR); strong metal−support interactions (SMSIs);

Monolithic nanoporous copper (NPC) ribbons can be fabricated through chemical dealloying of melt-spun Al−Cu alloys with 33−50 at % Cu under free corrosion conditions. The microstructure of these NPC ribbons was characterized using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, and transmission electron microscopy. The experimental results show that the melt-spun Al−Cu alloys with 33−50 at % Cu are composed of one or a combination of Al2Cu and AlCu intermetallic compounds. Both Al2Cu and AlCu can be fully dealloyed, and the synergetic dealloying of Al2Cu and AlCu in the two-phase Al−Cu alloys results in the formation of NPC with a homogeneous porous structure. The NPC ribbons exhibit an open, bicontinuous interpenetrating ligament-channel structure. NPC is a promising high strength/low density material due to its high porosity and yield strength of 86 ± 10 MPa. In addition, bulk NPC rods and slices can also be synthesized using the same strategy. These NPC ribbons, rods, and slices can serve as model materials to investigate the mechanical, physical (for example, electrical resistivity), and chemical properties associated with random porous structure of nanoporous solids.

Metallic actuators have recently aroused great interests, and alloying of noble element with earth-abundant metal is essential to lower the cost of actuation materials while keeping a significant strain response. Here, we report the design/fabrication of bulk nanoporous nickel-palladium alloy by dealloying. The alloy with a hierarchically porous structure shows different actuation behaviors in different electrolytes, which are correlated with the adsorption/desorption of hydrogen/hydroxyl and the nature (clean or oxide-cover) of ligament surface. The maximum reversible strain of the nickel-palladium actuator could reach 0.47% in potassium hydroxide solution, which is more competitive compared with other metallic actuation materials.The np-Ni80Pd20 with a hierarchically porous structure could trigger reversible strain of 0.47% in 1.0 M KOH solution.Download high-res image (153KB)Download full-size image

Development of excellent bi-functional electrocatalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) remains a key issue for the commercialization of various electrochemical devices such as fuel cells and metal-air batteries. Herein, we report the synthesis and electrocatalytic performance of mesoporous nanostructured spinel-type MFe2O4 (M = Co, Mn, Ni) oxides which can serve as alternative low-cost bi-functional electrocatalysts for ORR/OER. Loaded on XC-72 carbon support, the MFe2O4 spinel oxides show the M-dependent catalytic activities with CoFe2O4 being the most active electrocatalyst followed by MnFe2O4 and NiFe2O4 for ORR. For the OER, however, the activity increases in the order: MnFe2O4 < NiFe2O4 ≈ CoFe2O4. Additionally, the CoFe2O4 catalyst shows the smallest overpotential between ORR and OER. Compared with commercial IrO2, the MFe2O4 catalysts reveal comparable OER activities. Furthermore, the MFe2O4 catalysts exhibit much better methanol tolerance and stability than Pt/C. Meanwhile, both electrochemical measurements and density functional theory (DFT) calculations verify that the ORRs on the MFe2O4 catalysts are a direct 4 e− pathway in the alkaline solution, and expound the reason for the excellent methanol tolerance of MFe2O4.

CeO2 is widely used as a commercial CO oxidation catalyst, but it suffers from high-temperature (>200 °C) complete conversion. Despite enormous efforts made to promote its low-temperature activity by interfacing CuO and CeO2, it is still a long-standing challenge to balance the desired catalytic activity with high-yield preparation. Creating intimate synergistic interfaces between Cu and Ce species and exploring surfactant-free large-scale methods are both critical and challenging. To address these concerns, we synthesized highly active Cu doped CeO2 nanowires for low-temperature CO oxidation, relying on intentionally maneuvering precursor alloy compositions and a high-yield dealloying method. The favorable one-dimensional doping structure inherited from the nanowire bundles of the as-dealloyed precursors, clean surfaces and intimate synergistic effects between Cu and Ce contribute to excellent CO oxidation performances, with 5% room-temperature conversion triggered at 35 °C and 100% conversion at 100 °C. 96% of O2 selectivity at 88 °C in CO preferential oxidation was also obtained. The long-term durability for 24 hours at 100% CO conversion without any decay confirms the robust characteristics of the catalysts. Moreover, this work offers some insights into the reasonable design of alloy precursors to realize property-oriented alloys to nanowires batch transformation for the study of industrial catalysts.

It is a great challenge to design highly active, stable and low-cost catalysts for electrochemically splitting water to realize the clean energy generation and renewable energy storage. Herein, a facile one-step dealloying strategy was proposed to synthesize mesoporous CoFe-based oxides and layered double hydroxides (LDHs). Benefitting from the fast mass transfer and more active sites caused by the open mesoporous structure, the CoFe-based materials exhibit excellent electrocatalytic activities and stability towards the oxygen evolution reaction (OER) in an alkaline electrolyte (1 M KOH). The CoFe-LDH catalyst only needs an overpotential of 0.286 V to achieve 10 mA cm−2, and a small Tafel slope of 45 mV dec−1 for the OER. Moreover, an alkaline electrolyzer was constructed with the CoFe-LDH as both the anode and cathode. The electrolyzer delivers a current density of 10 mA cm−2 at a voltage of 1.69 V toward overall water splitting in the 1 M KOH solution.

One-dimensional (1D) nanostructures have been receiving significant attention due to their unique properties and potential applications. However, their low-cost, highly efficient synthesis remains a great challenge. Herein, we proposed a eutectic-directed self-templating strategy to synthesize PtNi nanoporous nanowires (NPNWs) through the combination of rapid solidification and dealloying. The eutectic-induced phase confinement and dealloying inheritance effect jointly favored the formation of PtNi NPNWs. The PtNi NPNWs exhibit superior electrocatalytic activity (5-fold enhancement in the specific activity) and enhanced durability towards oxygen reduction reaction, as benchmarked with commercial PtC. Moreover, the mechanisms for the activity enhancement have been rationalized on the basis of adsorption energy, d-band center, thermodynamics, and kinetics through density functional theory calculations.

•O22-/O- functionalized oxygen-deficient Co3O4 nanorods were facilely synthesized.•Co3O4 shows specific capacitance of 739 F g−1 with superior stability of 50,000 cycles.•Co3O4 shows overpotential of 275 mV for OER with stability of 300 h @ 100 mA cm−2.•The electrolyzer for overall water splitting can be driven by supercapacitors.Owing to high theoretical specific capacitance of 3560 F g−1 and intrinsic activity towards oxygen evolution reaction (OER), inexpensive Co3O4 is drawing much attention as either a promising pseudocapacitive electrode or OER catalyst. However, restricted to poor conductivity and lack of active sites, Co3O4 usually exhibits limited experimental capacitance and OER activity, barely satisfying high energy density delivering of supercapacitors and low energy input of water-splitting systems. Herein, we report O22-/O- functionalized oxygen-deficient Co3O4 nanorods for supercapacitor and water splitting dual applications. The CoC2O4·2H2O converted oxygen-deficient Co3O4 nanorods show enhanced electrical conductivity as confirmed by the increased carrier density. The increased number of Co2+ sites (oxygen vacancies) and CoOOH are believed to contribute to the improvement in faradaic reactions and OER activity. Additionally, surface functionalization by O22-/O- is realized in oxygen-deficient Co3O4 nanorods. On the basis of these merits, the as-synthesized Co3O4 nanorods demonstrate a significantly high specific capacitance of 739 F g−1 and an ultralow overpotential of 275 mV at 10 mA cm−2 for OER with ultralong stability of over 300 h (@ 100 mA cm−2). Specifically, an electrolyzer for overall water splitting can be driven by asymmetric supercapacitors with the optimized cobalt oxide as both electrocatalyst and electrode material.Download high-res image (246KB)Download full-size image

Metallic actuators (metallic muscles) have attracted a great deal of interest because of their potential advantages over piezoelectric ceramics and conducting polymers. However, to develop high performance actuators using earth's abundant and inexpensive metallic elements is a formidable challenge so far. Here, we report the design and fabrication of nickel-based actuators with low material cost (<1/2000 of gold), which demonstrate an unprecedented performance including giant reversible strain (up to 2%), ultrahigh work density (11.76 MJ m−3, the highest among the known actuator materials), and long cycle life (70% strain retention after 10000 cycles). This outstanding performance of the nickel-based actuators originates from their unique hierarchically nanoporous structure and the oxide-covered nature of the Ni surface.

Metal–hydrogen (in particular, Pd–H) interactions have been receiving considerable attention over the past 150 years within the scope of hydrogen storage, catalytic hydrogenation, hydrogen embrittlement and hydrogen-induced interfacial failure. Here, for the first time, we show that the coupling of hydrogen adsorption and absorption could trigger giant reversible strain in bulk nanoporous Pd (np-Pd) in a weakly adsorbed NaF electrolyte. The bulk np-Pd with a hierarchically porous structure and a ligament/channel size of ∼10 nm was fabricated using a dealloying strategy with compositional/structural design of the precursor. The np-Pd actuator exhibits a giant reversible strain of up to 3.28% (stroke of 137.8 μm), which is a 252% enhancement in comparison to the state-of-the-art value of 1.3% in np-AuPt. The strain rate (∼10−5 s−1) of np-Pd is two orders of magnitude higher than that of current metallic actuators. Moreover, the volume-/mass-specific strain energy density (10.71 MJ m−3/3811 J kg−1) of np-Pd reaches the highest level compared with that of previously reported actuator materials. The outstanding actuation performance of np-Pd could be attributed to the coupling of hydrogen adsorption/absorption and its unique hierarchically nanoporous structure. Our findings provide valuable information for the design of novel high-performance metallic actuators.

•We fabricate cobalt oxalate-anchored cobalt foil electrode through anodization.•The hybrid electrode presents superior specific capacitance of 1269 F g−1.•The hybrid electrode retains 91.9% after super-long cycling of 100,000 cycles.•The present electrode has excellent flexibility and good mechanical properties.•The asymmetric CoC2O4//AC supercapacitor shows high energy and power density.Transition metal oxalate materials have shown huge competitive advantages for applications in supercapacitors. Herein, nanostructured cobalt oxalate supported on cobalt foils has been facilely fabricated by anodization, and could directly serve as additive/binder-free electrodes for supercapacitors. The as-prepared cobalt oxalate electrodes present superior specific capacitance of 1269 F g−1 at the current density of 6 A g−1 in the galvanostatic charge/discharge test. Moreover, the retained capacitance is as high as 87.2% as the current density increases from 6 A g−1 to 30 A g−1. More importantly, the specific capacitance of cobalt oxalate retains 91.9% even after super-long cycling of 100,000 cycles. In addition, an asymmetric supercapacitor assembled with cobalt oxalate (positive electrode) and activated carbon (negative electrode) demonstrates excellent capacitive performance with high energy density and power density.

The electrochemically induced electrical resistance response of nanostructured metallic materials is an important issue in interdisciplinary fields including electrochemistry, physics and surface science. Nanoporous metals possess an open three-dimensional bicontinuous ligament (nanowire network)-channel (nanopore) structure with high surface-to-volume ratios, and show great potentials for investigations in this topic. Here we fabricate nanoporous silver (NPS) with high density of lattice defects (dislocations, twins, stacking defaults and grain boundaries) and ligaments composed of Ag nanocrystals with sizes comparable to the ligament length scale. More importantly, the present NPS shows extraordinarily enhanced reversible resistance response to electrochemical stimuli in alkaline electrolytes. A giant reversible resistance change of up to ∼1100% has been achieved in NPS. Moreover, the reversible electrical resistance change of NPS can be well modulated through cyclic voltammetry or square wave potential input. The related mechanisms have been rationalized on the basis of reversible oxide formation/reduction on the ligament surface of NPS, silver dissolution, as well as the effects of lattice defects in NPS.Nanoporous silver (NPS) fabricated by dealloying possesses large density of lattice defects (dislocations, twins, stacking defaults and grain boundaries) and ligaments composed of silver nanocrystals with sizes comparable to the ligament length scale. A giant reversible resistance of up to ∼1100% has been achieved for electrochemically induced response in NPS, which could be attributed to both the surface adsorption of chemical species and the aid of lattice defects.

The surface stress–charge coefficient, ζ, is a fundamental material parameter and reflects the response of surface stress to the change of superficial charge. The sign and the quantity of ζ play a crucial role in electrochemically induced actuation of nanostructured metals. Here, for the first time, we address the electrochemical actuation and the associated stress–charge coefficients of bulk nanoporous nickel (np-Ni) in both strongly (NaOH) and weakly (NaF) adsorbed electrolytes. The results reveal a normal negative value of ζ for the np-Ni with the clean surface, and unusual positive values of ζ for the oxide-covered surface. Interestingly, the oxidized np-Ni cannot recover the conventional negative value of ζ even in the cathodic potential window. Moreover, the reversible strain amplitude and the involved charge are quite different in distinct potential windows (the same electrolyte) or in different electrolytes (strongly or weakly adsorbed). In addition, density functional theory (DFT) calculations have been performed to understand the electrochemical actuation behaviors of the np-Ni with different surface states. In some aspects, the scenario of the np-Ni indeed differs from that of nanoporous noble metals like Au or Pt. Our findings provide useful information on understanding the electrochemical actuation of nanostructured metals, and novel actuators or sensors could be developed based upon earth-abundant metals like Ni, Co, and so forth.

•Np-PtPdCuAl catalysts were fabricated by dealloying AlCu-based precursor powders.•Nanoporous PtPdCuAl alloys show enhanced electrocatalytic properties for MOR and ORR.•Electrocatalytic properties of np-PtPdCuAl can be modified by controllable dealloying.Electrocatalysts are crucial materials for applications of direct methanol fuel cells (DMFCs). Here, we have designed a novel multi-component nanoporous alloy electrocatalyst, and further modified its electrocatalytic performance through a controllable dealloying strategy. The quaternary nanoporous PtPdCuAl (np-PtPdCuAl) alloys have been successfully fabricated by dealloying mechanically alloyed AlCuPdPt precursor. Well control of one-step or two-step dealloying allows to tune the compositions and electrocatalytic activities of the np-PtPdCuAl alloys (designated as T1–T6 alloys). The np-PtPdCuAl alloys obtained through two-step dealloying show much enhanced electrocatalytic properties towards methanol electro-oxidation reaction (MOR) and oxygen reduction reaction (ORR) in comparison to the commercial benchmark Pt/C catalyst. Moreover, the np-PtPdCuAl alloy with the best MOR and ORR properties as well as excellent CO tolerance could be obtained by firstly dealloying in the 2 M NaOH solution and then in the 1 M HNO3 solution (T3 alloy). This facile synthesis and easy control route is promising for the development of high performance electrocatalysts in DMFCs, and can be extended to fabricate other multi-component Pt-based catalysts with enhanced activities.Download high-res image (188KB)Download full-size image

•Nanoporous silver can be fabricated by chemical dealloying of Mg65Ag35 alloy.•Residual Mg decreases with dealloying time following an exponential decay formula.•Coarsening of NPS follows a nonlinear relationship with an exponent of ∼4.8.•The activation energy is 55.7 ± 2.9 KJ mol−1 for the chemical dealloying of Mg65Ag35.Microstructural and compositional evolution of nanoporous silver (NPS) during dealloying of rapidly solidified Mg65Ag35 alloy in the 1 wt% HCl solution has been investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray analysis. The amount of MgAg phase decreases and that of f.c.c. Ag increases with increasing dealloying time, and no intermediate phase occurs during dealloying. The residual Mg content in NPS decreases with increasing dealloying time, following an exponential decay formula. The coarsening of ligaments in NPS with dealloying time follows a nonlinear relationship, and the coarsening exponent (n) is ∼4.8 for the dealloying of Mg65Ag35. In addition, the activation energy is 55.7 ± 2.9 kJ mol−1 for the chemical dealloying of the rapidly solidified Mg65Ag35 alloy in the HCl solution.

•Hexagonal spinel-type Mn2AlO4 nanosheets were fabricated by dealloying/annealing.•The Mn2AlO4 nanosheets exhibit a high BET surface area of up to 164 m2 g−1.•Mn2AlO4 nanosheets show superior catalytic activity and methanol tolerance in ORR.•The RDE, RRDE and DFT results confirm the 4e− pathway for ORR on Mn2AlO4.Oxygen reduction reaction (ORR) is of crucial importance in fuel cells and metal–air batteries, however, the sluggish dynamics of ORR remains a critical issue to be addressed. Here, we report the preparation of hexagonal spinel-type Mn2AlO4 nanosheets with a high BET surface area of up to 164 m2 g−1 through a dealloying–annealing strategy. The Mn2AlO4 catalyst shows a good catalytic activity towards ORR in the alkaline solution, as well as much better methanol tolerance than the commercial Pt/C. Moreover, both the electrochemical measurements and density functional theory (DFT) calculations (adsorption energy, density of states, H2O2 decomposition) demonstrate that the ORR on Mn2AlO4 is a four-electron pathway. In addition, the DFT results expound the reason why the Mn2AlO4 catalyst has much better methanol tolerance than Pt/C.

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are crucial processes for energy conversion/storage systems, such as fuel cells, metal–air batteries, and water splitting. However, both reactions are severely restricted by their sluggish kinetics, thus requiring highly active, cost-effective, and durable electrocatalysts. Herein, we develop novel bifunctional nanocatalysts through surface nanoengineering of dealloying-driven nanoporous gold (NPG). Pd overlayers were precisely deposited onto the NPG ligament surface by epitaxial layer-by-layer growth. More importantly, the obtained NPG-Pd overlayer nanocatalysts exhibit remarkably enhanced electrocatalytic activities toward both the ORR and OER in alkaline media, benchmarked against a stateof- the-art Pt/C catalyst. The improved electrocatalytic performance is rationalized by the unique three-dimensional nanoarchitecture of NPG, enhanced Pd utilization efficiency from precise control of the Pd overlayers, and change in electronic structure, as revealed by density functional theory calculations.

Rechargeable lithium ion batteries (LIBs) have transformed portable electronics and will play a crucial role in transportation, such as electric vehicles. For higher energy storage in LIBs, two issues should be addressed, that is, the fundamental understanding of the chemistry taking place in LIBs and the discovery of new materials. Here we design and fabricate two-dimensional (2D) WS2 nanosheets with preferential [001] orientation and perfect single crystalline structures. Being used as an anode for LIBs, the WS2-nanosheet electrode exhibits a high specific capacity, good cycling performance and excellent rate capability. Considering the controversy in the lithium storage mechanism of WS2, ex-situ X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS) analyses clearly verify that the recharge product (3.0 V vs. Li+/Li) of the WS2 electrode after fully discharging to 0.01 V (vs. Li+/Li) tends to reverse to WS2. More remarkably, the [001] preferentially-oriented 2D WS2 nanosheets are also promising candidates for applications in photocatalysis, water splitting, and so forth.

As promising electrode materials for electrochemical supercapacitors, pseudocapacitive transition metal oxides such as NiO possess high theoretical specific capacitance, environmental benignity and good abundance. However their areal capacitance and cycling stability are greatly restricted by their poor electronic conductivity (NiO, 10−2 to 10−3 S cm−1). Here we propose an in situ growth strategy in combination with nanoscale design to construct ultrathin mesoporous NiO nanosheets on a 3D network of nickel foam. The hybrid structures show well enhanced conductivity and ion transfer, giving rise to an ultrahigh specific capacitance of 2504.3 F g−1 which is close to the theoretical value of NiO. The electrodes also exhibit remarkable cycling stability (no degradation of the overall capacitance after 45000 cycles). The amazing electrochemical performance of such hybrid structures makes them potential electrodes in supercapacitors. The present strategy could be popularized in other transition metal oxides like Co3O4, MnO2, etc. to create electrodes with desirable nanostructures.

Highly sensitive and efficient biosensors play a crucial role in clinical, environmental, industrial, and agricultural applications, and tremendous efforts have been dedicated to advanced electrode materials with superior electrochemical activities and low cost. Here, we report a three-dimensional binder-free Cu foam-supported Cu2O nanothorn array electrode developed via facile electrochemistry. The nanothorns growing in situ along the specific direction of <011> have single crystalline features and a mesoporous surface. When being used as a potential biosensor for nonenzyme glucose detection, the hybrid electrode exhibits multistage linear detection ranges with ultrahigh sensitivities (maximum of 97.9 mA mM–1 cm–2) and an ultralow detection limit of 5 nM. Furthermore, the electrode presents outstanding selectivity and stability toward glucose detection. The distinguished performances endow this novel electrode with powerful reliability for analyzing human serum samples. These unprecedented sensing characteristics could be ascribed to the synergistic action of superior electrochemical catalytic activity of nanothorn arrays with dramatically enhanced surface area and intimate contact between the active material (Cu2O) and current collector (Cu foam), concurrently supplying good conductivity for electron/ion transport during glucose biosensing. Significantly, our findings could guide the fabrication of new metal oxide nanostructures with well-organized morphologies and unique properties as well as low materials cost.Keywords: biosensors; catalysis; hybrid materials; nanostructures; nanothorn arrays

Atomic layer-by-layer construction of Pd on nanoporous gold (NPG) has been investigated through the combination of underpotential deposition (UPD) with displacement reaction. It has been found that the UPD of Cu on NPG is sensitive to the applied potential and the deposition time. The optimum deposition potential and time were determined through potential- and time-sensitive stripping experiments. The NPG-Pd electrode shows a different voltammetric behavior in comparison to the bare NPG electrode, and the deposition potential was determined through the integrated charge control for the monolayer UPD of Cu on the NPG-Pd electrode. Five layers of Pd were constructed on NPG through the layer-by-layer deposition. In addition, the microstructure of the NPG-Pdx (x = 1, 2, 3, 4 and 5) films was probed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). The microstructural observation demonstrates that the atomic layers of Pd form on the ligament surface of NPG through epitaxial growth, and have no effect on the nanoporous structure of NPG. In addition, the hydrogen storage properties of the NPG-Pdx electrodes have also been addressed.

Metal oxides possess high theoretical specific capacitance, but their pseudocapacitive properties are restricted by the poor electronic conductivity. Here we present a strategy to synthesize a three-dimensional binder/conducting agent-free nickel oxide (NiO) electrode through the combination of anodization with calcination. The NiO electrode is composed of a 3D conductive nickel network decorated with nanopetal-like NiO arrays. The influence of calcination temperature has been investigated, with respect to the microstructure and pseudocapacitive properties of the NiO electrodes. The NiO electrode demonstrates great electrochemical properties, especially remarkable rate capability (82% retention of the highest value for the 25-fold enhanced current density) and cycling stability (good capacitance retention after 30000 cycles). Moreover, an asymmetric supercapacitor has been assembled using NiO as the positive electrode and activated carbon (AC) as the negative electrode. The NiO//AC supercapacitor presents excellent cycling stability (91.3% retention after 10000 cycles), and could power a mini fan as well as a commercial red LED for more than 270 min.

Nanostructured transition metal oxides have been investigated extensively for supercapacitor electrodes due to their high theoretical specific capacitance, low-cost, environment benignity and abundance. However, pristine transition metal oxides suffer from difficulty of synthesis, poor electronic conductivity and mechanical flexibility. In this work, we report a facile, low-cost and high-throughput synthesis of hierarchical structure which consists of cuprous oxide (Cu2O) microsphere-nanosheets on the surface of flexible Cu foil (namely Cu2O@Cu) via a two-step electrochemical method (anodization and electro-oxidation). The influence of the anodization parameters on surface roughness of Cu foil has been investigated, and the optimum anodization procedure was determined to be 50 V for 4 cycles. This Cu2O@Cu electrode exhibits excellent capacitance properties, such as up to 390.9 mF cm−2 at 2 mA cm−2 in areal capacitance, and high flexibility, as observed by cyclic voltammetry measurement under various deformation (bending and folding) situations. Furthermore, the Cu2O@Cu electrode presents superior long-term cycling stability over 100000 cycles, with the capacitance retention of over 80%. The present binder-free Cu2O@Cu microsphere-nanosheets electrode is highly promising for future applications in flexible supercapacitors.

Here we report a facile efficient anodization approach to fabricate nickel oxalate nanostructures on nickel foam (NON@NF). The NON@NF electrode exhibits high specific capacitance and excellent cycling performance. Moreover, an assembled asymmetric supercapacitor based upon NON@NF and activated carbon shows excellent performance with high energy/power density and long cycling stability.

Here we report the preparation of 3D binder-free NiO nanorod-anchored Ni foam electrodes, and their application as anode materials for rechargeable lithium-ion batteries. By anodization followed by thermal annealing, blooming flower-like NiO arrays were anchored to Ni foam, and were characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and N2 adsorption–desorption experiments. Electrochemical properties were evaluated by cyclic voltammetry (CV) and galvanostatic cycling. Cycling performance shows that after 70 cycles the NiO nanorod-anchored Ni foam electrode can still deliver a stable reversible capacity up to 705.5 mA h g−1 and 548.1 mA h g−1 with a high coulombic efficiency (≥98%) at a constant current density of 1 A g−1 and 2 A g−1, respectively. The superior performance of the NiO electrode can be attributed to its favorable morphology and the excellent electrical contact between NiO and the current collector of Ni foam. The present strategy can be extended to fabricate other self-supported transition metal oxide nanostructures for high-performance lithium-ion batteries.

Nanostructured Cu oxides/hydroxides are promising materials for supercapacitors because of their high theoretical capacitance, low cost and friendliness to environment. However, the development of commercially viable Cu oxides/hydroxides with superior capacitive performance is still challenging. Here, 3D binder-free Cu2O@Cu nanoneedle arrays electrode was developed via facile electrochemistry. The electrode exhibits a high capacitance of 862.4 F g−1 and excellent cycling stability (20000 cycles). Furthermore, we have successfully constructed a Cu2O@Cu//AC asymmetric supercapacitor, which can achieve an energy density of 35.6 W h kg−1 at 0.9 kW kg−1 and excellent stability with a capacitance retention of 92% after 10000 cycles. After being charged for dozens of seconds, the in-series Cu2O@Cu//AC supercapacitors can light up LED arrays and even charge a mobile phone. These fascinating performances reasonably indicate their potential in commercial applications for energy storage.

•Multi-component np-alloy can be fabricated by ball-milling and two-step dealloying.•Np-PtPdAlCu alloy shows ultrafine three-dimensional ligament/channel structure.•Np-PtPdAlCu alloy shows excellent electrocatalytic performance for DMFCs.In this paper, we explore nanoporous PtPdAlCu (np-PtPdAlCu) quaternary alloy through ball-milling with the subsequent two-step dealloying strategy. The microstructure and catalytic performance of the np-PtPdAlCu catalyst have been characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electrochemical measurements. The np-PtPdAlCu catalyst exhibits an open bi-continuous interpenetrating ligament/channel structure with a length scale of 2.3 ± 0.5 nm. The np-PtPdAlCu catalyst shows 2 and 3.5 times enhancement in the mass activity and area specific activity towards methanol oxidation at anode respectively, compared to the Johnson Matthey (JM) Pt/C (40 wt.%) catalyst. Moreover, the CO stripping peak of np-PtPdAlCu is 0.49 V (vs. SCE), indicating a 180 mV negative shift in comparison with the Pt/C catalyst (0.67 V vs. SCE). In addition, the np-PtPdAlCu catalyst also shows an enhanced oxygen reduction reaction (ORR) activity at cathode compared to Pt/C. The present study provides a facile and effective route to design high-performance catalysts for direct methanol fuel cells (DMFCs).Ultrafine nanoporous multiple-component alloy with enhanced performance for DMFCs is fabricated by mechanical alloying and subsequent two-step dealloying.

Nanoporous Cu–O system catalysts with different oxidation states of Cu have been fabricated through a combination of dealloying as-milled Al66.7Cu33.3 alloy powders and subsequent thermal annealing. X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) have been used to characterize the microstructure and surface chemical states of Cu–O catalysts. The peculiar nanoporous structure can be retained in Cu–O catalysts after thermal treatment. Catalytic experiments reveal that all the Cu–O samples exhibit complete CO conversion below 170 °C. The optimal catalytic performance could be achieved through the combination of annealing in air with hydrogen treatment for the Cu–O catalyst, which shows a near complete conversion temperature (T90%) of 132 °C and an activation energy of 91.3 KJ mol−1. In addition, the present strategy (ball milling, dealloying and subsequent thermal treatment) could be scaled up to fabricate high-performance Cu–O catalysts towards CO oxidation.

•CO oxidation can be achieved over unsupported np-Ag catalyst without heat-treatment.•Residual Mg has no influence on catalytic activity of np-Ag catalyst.•Np-Ag catalysts show a size-dependent catalytic activity towards CO oxidation.•Unsupported np-Ag catalysts possess a good catalytic activity towards CO oxidation.This work discussed the catalytic performance towards CO oxidation over unsupported nanoporous Ag (np-Ag) catalysts synthesized by dealloying of Mg77Ag23 (at.%) alloy under controllable etching conditions. The np-Ag catalysts were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) analysis, X-ray photoelectron spectroscopy (XPS) and UV-vis diffuse reflectance spectroscopy (UV-vis DRS). The np-Ag catalysts exhibit an open, bicontinuous interpenetrating ligament-channel structure. The np-Ag samples fabricated under different conditions possess distinct feature sizes ranging from ∼15.7 to ∼142.6 nm. Without any heat-treatment, the as-obtained np-Ag catalysts were utilized for catalysis tests. The results reveal that the catalytic activity of the unsupported np-Ag catalysts is comparable with or even better than that of supported Ag catalysts with heat-treatment. In addition, the role of residual Mg and feature size in the catalytic activity of the np-Ag catalysts has been clarified. The catalytic mechanism of the present unsupported np-Ag catalysts has also been discussed.

Here, we report the fabrication of ultrafine nanoporous PdFe/Fe3O4 electrocatalysts by a facile dealloying strategy. The results show that the phase formation of the as-dealloyed samples is dependent upon the Pd:Fe atomic ratio in the Al–Pd–Fe ternary precursors. The size of ligaments is as small as ∼2 nm in the nanoporous structure of the as-dealloyed samples, which is the smallest among the literature data reported for nanoporous metals/alloys. The present nanoporous PdFe/Fe3O4 nanocomposites show excellent electrocatalytic activities towards the oxidation of methanol and ethanol in alkaline media due to the double enhancement from Fe3O4 and Fe in PdFe. In addition, the nanoporous PdFe/Fe3O4 sample dealloyed from the Al75Pd12.5Fe12.5 precursor exhibits the highest electrocatalytic activity. These materials are potential anode electrocatalysts for applications in direct alcohol fuel cells.

The chemical dealloying of bi-phase Al-35Ag alloy has been investigated within the parting limit. The dealloying of α-Al(Ag) and Ag2Al commenced simultaneously, and all α-Al(Ag) and part of Ag2Al were dealloyed, leaving residual Ag2Al to be dealloyed afterwards. The dealloying of the residual Ag2Al is associated with vacancy controlled mechanism and diffusion of Al atoms. It is revealed that the diffusions of the Al and Ag atoms during dealloying are significant. The Ag skeletons formed at the initial stage, and became coarsened gradually with a time dependence of d ∝ t2/5, illustrating the vital role of diffusion of Ag atoms.Highlights► Selective leaching of α-Al(Ag) and Ag2Al occurs simultaneously during dealloying. ► Diffusion of Al and vacancy controlled mechanism dominate the etching of Ag2Al. ► The coarsening of ligaments in NPS follows a time dependence of d ∝ t2/5.

The anodization of a gold electrode in oxalic acid aqueous solution of different concentration has been investigated at different applied potentials, which enables the formation of nanoporous gold (NPG). Electrochemical measurements show that the electrochemically active surface areas of the as-anodized Au samples show an obvious potential, electrolyte concentration and time dependence. The as-prepared NPG samples were used as the working electrode to investigate the redox behavior of p-nitrophenol (p-NP) by cyclic voltammetry (CV). The CV profiles of NPG display a pair of redox peaks, and the peak current densities increase linearly with increasing p-NP concentration. Besides, o-nitrophenol (o-NP) has little influence on the electrochemical detection of p-NP. Through the anodization strategy, NPG electrodes with a high sensitivity and good selectivity can be developed to detect trace p-NP in water.

We present a facile one-step dealloying strategy to fabricate novel nanoporous silver (NPS)/Fe3O4 nanocomposites with tunable magnetism and excellent antibacterial ability. The NPS/Fe3O4 nanocomposites were obtained by chemically dealloying rapidly solidified Al–Ag–Fe precursors in a 20 wt% NaOH solution. The microstructure of the NPS/Fe3O4 nanocomposites has been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, transmission electron microscopy (TEM) and high resolution TEM (HRTEM) with nanobeam-EDX (NB-EDX). In the nanocomposites, the NPS matrix exhibits an open bicontinuous interpenetrating ligament–channel structure, with ligament/channel sizes of 20–50 nm, and the embedded Fe3O4 particles are octahedral and several hundred nanometers in size. Through changing the Ag/Fe atomic ratio in the Al–Ag–Fe precursors, we can tune the magnetic properties of the NPS/Fe3O4 nanocomposites. Antibacterial tests demonstrate that the NPS/Fe3O4 nanocomposites show excellent antibacterial activities against E. coli K12 and the embedded Fe3O4 makes these materials magnetically recyclable. The present NPS/Fe3O4 nanocomposites are potential antibacterial materials with a magnetically recyclable property.

•Nanoporous PdAu catalyst can be fabricated by dealloying of AlPdAu ternary alloy.•Nanoporous PdAu catalyst exhibits enhanced activity for methanol electro-oxidation.•Alloying Au facilitates CO-like species oxidation and active Pd sites recovery.Nanoporous PdAu catalyst (NP-PdAu) can be fabricated by chemical dealloying ternary AlPdAu alloy in the alkaline solution. Electrochemical measurements demonstrate that the NP-PdAu exhibits greatly enhanced catalytic activity and long-term stability toward methanol electro-oxidation. The as-revealed specific activity and mass activity can attain to 1.30 mA cm−2 and 866.50 mA mg−1 (Pd), respectively, which is significantly higher than that of monometallic NP-Pd, NP-Au and widely-reported Pd or Pd-based nanoparticle catalysts. Moreover, methanol oxidation reaction on the NP-PdAu electrode is diffusion-controlled and represents a good linear correlation with methanol concentration. The results indicate that NP-PdAu is attractive as a promising electrocatalyst of alkali-type direct methanol fuel cells (DMFCs).

The anodization of Pd in H2SO4 solutions has been investigated by electrochemical measurements, considering the effect of the applied potential, polarization time, and electrolyte concentration. The anodization and subsequent reduction result in the formation of Pd nanostructures on the electrode surface. Compared to the bulk Pd, the anodization of Pd in H2SO4 solutions leads to different cyclic voltammetry (CV) behaviors including well-separated adsorption/desorption peaks in the hydrogen region and relatively larger reduction peak areas. The improvement of electrochemically active surface areas (EASAs) of the anodized Pd samples is strongly dependent upon the electrolyte concentration, and the optimum H2SO4 concentration is 1.0 M. Both the applied potential and polarization time have a significant influence on the anodization process of Pd. For the given electrolyte concentration, there exist desirable applied potential and polarization time to achieve greater EASAs. The EASAs of the anodized Pd obtained under the optimum polarization conditions can reach as large as 890 times compared to its geometric area. In addition, the formation mechanism of Pd nanostructures on the electrode surface has been discussed on the basis of microstructural analysis. The present findings provide a promising route to fabricate nanostructured Pd electrocatalysts with ultrahigh EASAs.Keywords: anodization; cyclic voltammetry; electrochemically active surface areas (EASAs); nanostructure; Pd; potentiostatic polarization;

The anodization of Pd in a 1.0 M H2SO4 solution has been investigated, which enables spontaneous formation of Pd nanoparticles. Electrochemical measurements show that the anodized Pd exhibits significantly larger electrochemically active surface area (EASA) and excellent catalytic activity towards electro-oxidation of methanol, ethanol, and formic acid in comparison to the flat Pd. The electro-catalytic activity of the anodized Pd is ca. 260 and 210 times higher than that of the flat Pd for the oxidation of methanol and ethanol in the alkaline media, respectively. Moreover, the anodized Pd presents superior steady-state activity for the diffusion-controlled electro-oxidation of methanol, and the anodization greatly enhances the intrinsic catalytic activity of each Pd atom. The anodized Pd will be a promising candidate for anode catalysts of fuel cells.Highlights► Pd nanostructure forms by anodization/CV reduction in 1.0 M H2SO4 solution. ► The EASA of Pdanod. is approximately 44 times that of Pdflat. ► Activity of Pdanod. is 260 times higher than that of Pdflat for methanol oxidation. ► Activity of Pdanod. is 210 times higher than that of Pdflat for ethanol oxidation. ► Simple way to increase catalytic activity of Pd anode for fuel cells is presented.

The dealloying behavior of bi-phase Al–Ag alloys in 5 wt.% HCl in non-treated and magnetic treated conditions was comparatively investigated. The as-dealloyed samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) analysis coupled with SEM. The results reveal that an external magnetic field would accelerate the dealloying process and the as-dealloyed samples from magnetic treatment are characterized by a finer and more homogeneous three dimensional (3D) bi-continuous nanoporous structure compared with those from non-treatment dealloying. The smaller diffusion coefficient (Ds) of silver and the larger diffusion activation energy (Eα) under a magnetic field can be responsible for the finer nanoporous structure. It is deemed that the formation of diamagnetic reaction products (during the etching of Al) and the crystal nucleation of silver (during the dealloying of Ag2Al) are accelerated by the external magnetic field. In addition, not only the pre-exponential factor (D0), obtained from the Arrhenius equation for diffusion of Ag, but also the activation energy (Eα) were influenced by the magnetic field, implying that different diffusion mechanisms and also the complicated underlying dealloying mechanism were involved.

Nanoporous Cu powders have been fabricated through mechanical alloying and subsequent dealloying. The ligament/channel size of as small as 21.3 ± 2.7 nm has been obtained by dealloying as-milled Al–Cu powders in a NaOH solution at room temperature, and can be tuned by changing the dealloying temperature. The surface diffusivity of Cu adatoms and mean activation energy have been evaluated based upon surface diffusion controlled coarsening mechanism.

In the present work, the dealloying of Al–Au-based precursors and formation of nanoporous Au-based alloys have been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM) and energy dispersive X-ray (EDX) analysis. The results show that the addition of Ni and/or Co has no influence on phase constitution of rapidly solidified Al–Au–M (M = Ni, Co, or Ni/Co) alloys and a single-phase Al2(Au,M) intermetallic compound can be identified in these ternary and quarternary precursor alloys. The Al–Au-based precursors can be fully dealloyed in an alkaline solution under free corrosion conditions, and the dealloying results in the formation of novel ultrafine nanoporous Au-based alloys (Au(Ni), Au(Co) and Au(Ni,Co)) with ligaments/channels of ∼5 nm. The ultrafine nanoporous Au-based alloys possess extraordinarily high structural stability against thermal annealing. Moreover, due to the intrinsic magnetism of Ni and Co, the addition of Ni and/or Co leads to the formation of novel magnetic nanoporous alloys. The dealloying mechanism of these Al–Au-based precursors has been discussed based upon surface diffusion of Au adatoms and interaction between Au and additional elements. The present findings provide a new dealloying route to fabricate ultrafine nanoporous Au-based alloys with high stability and magnetic properties through alloy design of precursors.

We present a facile two-step strategy to fabricate a novel nanoporous core–shell Cu@Cu2O nanocomposite photocatalyst. The photocatalyst was synthesized via the combination of dealloying of the as-milled Al66.7Cu33.3 (at.%) precursor powders in alkaline media with subsequent surface oxidation in air. The microstructure of the as-prepared photocatalyst has been characterized by X-ray diffraction (XRD), a field-emission scanning electron microscope (FESEM) and a transmission electron microscope (TEM). The results show that the as-prepared photocatalyst exhibits an open, bicontinuous interpenetrating ligament (ca. 30 nm)–channel (ca. 15 nm) structure, and is comprised of Cu (core) and Cu2O (shell) phases. Methyl orange (MO) was used as the model pollutant, and photodegradation experiments were monitored by UV-vis spectrophotometry. The nanoporous core–shell Cu@Cu2O photocatalyst shows excellent photocatalytic activity towards the degradation of MO under sunlight. The MO degradation rate can reach as high as 8.04 mg min−1 gcat−1. In addition, the influence of additive amounts of photocatalyst and initial concentrations of MO on the photodegradation process has been investigated. The photodegradation mechanism of the as-prepared photocatalyst has also been discussed.

In this work, the dealloying of ternary Mg–Cu–Pd alloys and formation of nanoporous Cu–Pd alloys have been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution TEM (HRTEM), energy dispersive X-ray (EDX) analysis and electrochemical measurements. The results show that the Pd addition has a significant influence on the phase constitution and dealloying process of the rapidly solidified Mg–Cu–Pd alloys. Ultrafine nanoporous Cu–Pd alloy nanostructures with ligaments/channels of less than 10 nm can be obtained in the as-dealloyed samples. The dealloying mechanism and formation of ultrafine nanoporous structures have been rationalized by electrochemical activity measurements and surface diffusion of Cu/Pd adatoms. These ultrafine nanoporous Cu–Pd alloys exhibit high specific surface areas and superior electrocatalytic performance towards electro-oxidation of methanol and ethanol in alkaline media. The present findings provide a facile dealloying route to fabricate nanoporous Cu–Pd alloy electrocatalysts for applications in direct alcohol fuel cells.

The electrochemical dealloying of single-phase Al2Au alloy in 1 M sodium halide (NaF, NaCl, NaBr and NaI) aqueous solutions at 270, 290 and 340 K has been systematically investigated in this work. The effects of halide ions and temperature on the dealloying behavior have been studied with electrochemical methods like open-circuit potential measurements and dynamic polarization tests. Nanoporous gold (NPG) with a typical three-dimensional, bicontinuous, interpenetrating ligament-channel structure can be obtained from the single-phase Al2Au alloy by electrochemical dealloying in the NaCl, NaBr, and NaI solutions. In addition, the dealloyed NPG samples and the samples after coarsening at ambient conditions were characterized using field-emission scanning electron microscopy (FESEM). Morphological features like cracks and ligament sizes in NPG have been discussed. Furthermore, NPG samples that were almost free of cracks have been successfully prepared in the NaI solution at 340 K. Besides, based on the surface diffusion controlled coarsening mechanism, the surface diffusivities of gold adatoms along the alloy–electrolyte interfaces during dealloying have been evaluated in this work, as well as the activation enthalpy and activation entropy.

A novel Raney-like nanoporous Pd catalyst has been fabricated through the combination of ball-milling with alkali-dealloying strategy. The microstructure of this catalyst has been characterized using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results show that the as-fabricated Raney Pd powders are several microns in size, and each particle exhibits an open, bicontinuous interpenetrating ligament-channel structure with a length scale of 3–7 nm. Electrochemical measurements demonstrate that this Raney Pd catalyst has a high electrochemical active surface area and shows remarkable electrocatalytic activity and stability towards ethanol oxidation. Due to the advantages of simple preparation and superior performance, this Raney Pd catalyst can find promising application as a candidate for the anode catalyst of direct ethanol fuel cells.Highlights► Ball-milling and alkali-dealloying of Al-Pd can be used to produce Raney Pd catalyst. ► Powder-shaped configuration provides a high electrochemical active surface area. ► Raney Pd catalyst shows superior activity towards ethanol electro-oxidation.

In the present Article, we have investigated the microstructure, composition, and porosity evolution of nanoporous alloy during successive dealloying of ternary Al75Pd17.5Au7.5 precursor in NaOH/HCl and HNO3 aqueous solutions. The results show that the selective dissolution of Al through the first-step dealloying contributes to the formation of Pd–Au nanoporous composites, which are composed of two distinct structures: the finer nanoporous AuPd dendrites derived from the dealloying of Al2(Au,Pd) and the coarser nanoporous Pd(Au) derived from the dealloying of Al3(Pd,Au). Moreover, compared with those dealloyed in the 20 wt % NaOH solution, the Pd–Au nanocomposites exhibit a coarser length scale of ligaments/channels in the 5 wt % HCl solution. After the second-step dealloying in the 65 wt % HNO3 solution, the nanoporous Pd(Au) dissolves away, and the Pd dissolution results in the formation of Au-rich nanoporous alloy with bimodal channel size distributions. Nanoporous alloys with unique structures and compositions can be fabricated by dealloying based on alloy design and control over selective dissolution of elements in suitable electrolytes.

Electrochemical dealloying of a single-phase Al2Au alloy in sodium chloride solutions has been investigated considering influence of potential and electrolyte concentration. Both open-circuit potentials and corrosion potentials of Al2Au decrease with increasing electrolyte concentration and temperature. The overpotential and electrolyte concentration have a significant influence on dealloying behaviors of Al2Au, such as steady-state current density and dealloying duration. Nanoporous gold (NPG) can be fabricated by potentiostatic dealloying of Al2Au in the NaCl solutions. Moreover, surface diffusion evaluation demonstrates that there exist good linear relationships between the logarithm of surface diffusivities of Au adatoms (Auad) and overpotential, and between the surface diffusivities of Auad and electrolyte concentration. In addition, the activation energy decreases with increasing overpotential or chloride ion concentration.

In the present work, a green and simple strategy has been proposed to fabricate novel bi-modal nanoporous bimetallic Pt–Au alloy by electrochemical dealloying of a ternary Al75Pt15Au10 precursor in a neutral sodium chloride solution. The Al75Pt15Au10 precursor is composed of a single Al2(Pt,Au) phase with lattice vacancies inside. The bi-modal nanoporous Pt–Au alloy exhibits an island-channel structure and the islands show an ultrafine three-dimensional bicontinuous interpenetrating ligament-channel (∼3.5 nm) characteristic. The dealloying mechanism of the precursor and the formation of the nanoporous structure have been addressed using electrochemical measurements (potentiodynamic and potentiostatic polarization) and microstructural analysis (scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray analysis). The dealloying at the low potential of −0.4 V vs.Ag/AgCl is associated with the partial dissolution of Al and the disappearance of the vacancies, leading to the formation of the stoichiometric Al2(Pt,Au). The subsequent dealloying at 0.6 V vs.Ag/AgCl is related to the complete dissolution of Al and surface diffusion of Pt/Au, resulting in the formation of the ultrafine nanoporous structure. Besides, the bi-modal nanoporous Pt–Au alloy shows superior catalytic activity towards the electro-oxidation of formic acid in the acid media in comparison to the commercial JM-Pt/C catalyst. Our present findings provide implications for green synthesis of novel multi-functional nanoporous alloys through the electrochemical dealloying strategy in benign neutral salt solutions under mild conditions.

In the present study, magnetic nanoporous Cu(NPC)/(Fe,Cu)3O4 composites with tunable magnetism and excellent conductivity were fabricated by a facile one-step dealloying process. Three ternary Al–Cu–Fe alloys with different compositions were chosen as the precursors to carry out the dealloying process in a 20 wt% NaOH solution under free corrosion conditions. The microstructure of these NPC/(Fe,Cu)3O4 composites have been characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, transmission electron microscopy (TEM), and high resolution transmission electron microscopy (HRTEM) with nanobeam-EDX (NB-EDX). These NPC/(Fe,Cu)3O4 composites are composed of a NPC matrix with ligament/channel sizes of 20–40 nm and octahedral (Fe,Cu)3O4 embedded particles of 600–800 nm. The formation of these composites has been discussed based upon the surface diffusion of Cu adatoms and oxidation of Fe/Cu adatoms during dealloying. The N2 absorption/desorption results show that the NPC/(Fe,Cu)3O4 composites have a high surface area of up to 25.24 m2 g−1. The maximum values of the magnetic parameters of these NPC/(Fe,Cu)3O4 composites can reach 27.3 emu g−1, 7.7 emu g−1 and 218.5 Oe for the saturation magnetization, remanence and coercivity, respectively. The magnetic properties and the ratio of NPC:(Fe,Cu)3O4 in the NPC/(Fe,Cu)3O4 composites can be tuned by simply changing the Cu/Fe ratio in the Al–Cu–Fe precursor alloys, while keeping their excellent electrical conductivity. These functional composites will find potential applications in sensors, information storage, medical diagnostics, and so forth.

We present a facile route to fabricate novel nanoporous bimetallic Pt–Au alloy nanocomposites by dealloying a rapidly solidified Al75Pt15Au10 precursor under free corrosion conditions. The microstructure of the precursor and the as-dealloyed sample was characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and energy dispersive X-ray (EDX) analysis. The Al75Pt15Au10 precursor is composed of a single-phase Al2(Au,Pt) intermetallic compound, and can be fully dealloyed in a 20 wt.% NaOH or 5 wt.% HCl aqueous solution. The dealloying leads to the formation of the nanoporous Pt60Au40 nanocomposites (np-Pt60Au40 NCs) with an fcc structure. The morphology, size and crystal orientation of grains in the precursor can be conserved in the resultant nanoporous alloy. The np-Pt60Au40 NCs consist of two zones with distinct ligament/channel sizes and compositions. The formation mechanism of these np-Pt60Au40 NCs can be rationalized based upon surface diffusion of more noble elements and spinodal decomposition during dealloying. Electrochemical measurements demonstrate that the np-Pt60Au40 NCs show superior catalytic activity towards the electro-oxidation of methanol and formic acid in the acid media compared to the commercial JM-Pt/C catalyst. This material can find potential applications in catalysis related areas, such as direct methanol or formic acid fuel cells. Our findings demonstrate that dealloying is an effective and simple strategy to realize the alloying of immiscible systems under mild conditions, and to fabricate novel nanostructures with superior performance.

Nanocrystalline Pd40Ni60 alloy catalyst has been fabricated by dealloying a ternary Al75Pd10Ni15 alloy in a 20 wt.% NaOH aqueous solution under free corrosion conditions. The microstructure and catalytic performance of the catalyst have been characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and cyclic voltammetry. The Pd40Ni60 alloy consists of nanocrystals with sizes of 5–10 nm, and Pd/Ni elements exist in a solid solution form. Moreover, nanocrystalline zones, amorphous zones and lattice distortion can be observed in the Pd40Ni60 alloy. Electrochemical measurements demonstrate that, for equivalent mass Pd, Pd40Ni60 has an enhanced electrocatalytic performance towards methanol and ethanol oxidation in alkaline media than nanoporous Pd. The nanocrystalline Pd40Ni60 alloy is a promising catalyst towards alcohol oxidation in alkaline media for fuel cell applications.Highlights► Nanocrystalline PdNi alloy can be fabricated by dealloying Al75Pd10Ni15 precursor. ► PdNi alloy shows an enhanced catalytic activity towards alcohol electro-oxidation. ► The enhanced performance can be attributed to the alloying of Pd with Ni.

In this paper, the influence of alloy composition, dealloying solution and elemental doping on the dealloying process of rapidly solidified Mg–Ag based alloys and the formation of nanoporous silver (NPS) has been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and transmission electron microscopy (TEM). The results show that NPS and nanoporous silver-palladium (NPS–Pd) alloys can be fabricated by dealloying the Mg–Ag based alloys in acid media under free corrosion conditions. The NPS and NPS–Pd exhibit an open, three-dimensional bicontinuous interpenetrating ligament-channel structure. Furthermore, alloy composition and phase constitution of the Mg–Ag precursors have a significant influence on the ligament/channel size and the formation of cracks in NPS. The length scales of ligaments/channels in NPS can be tuned by simply changing the dealloying solution. Crack-free NPS with good mechanical integrity and small ligament/channel sizes can be obtained by dealloying the Mg–Ag alloys in suitable acid solutions. Moreover, the addition of Pd into Mg–Ag has a significant influence on the dealloying process and results in the formation of ultrafine bimodal NPS–Pd with ligaments/channels of ∼5 nm. The NPS–Pd alloy shows excellent hydrogen sensing properties with stable sensitivity, fast response and low detection limit. Our present findings provide implications for control and functionalization of nanoporous metals or alloys by alloy design, selection of dealloying media and elemental doping.

The dealloying of rapidly solidified Mg–Ag alloys with 50–65 at% Mg was performed in HCl solution. The precursor alloys are composed of a single MgAg phase with different vacancy content which exhibits dominant influence on the dealloying process. A vacancy-controlled dealloying mechanism is proposed based on a layer-by-layer model.

The dealloying processes of Al-Ag alloy ribbons consisting of two distinct phases of α-Al (Ag) and Ag2Al in the 5 wt.% H2SO4, 10 wt.% H3PO4, 10 wt.% C2H2O4 and 5 wt.% HCl solutions were investigated. The as-dealloyed samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) analysis coupled with SEM. It has been found that the resultant microstructure of the as-dealloyed samples is significantly influenced by the initial alloy composition and the acid kind. The four acid solutions are all able to leach out the Al from both the α-Al (Ag) and Ag2Al phases and the as-dealloyed samples exhibit the typical three dimensional (3D) bi-continuous nanoporous structure. The dealloying duration in four acid solutions ranges from 1.1 to 24 h, and the dealloying rates are influenced by acidity, acid concentration, and the diffusion coefficient (Ds) of Ag atoms which is affected by anions and interactions between anions and Al atoms. The specific surface area of the nanoporous silver (NPS) from the Al-15 at.% Ag alloy dealloyed in HCl was determined as 3.47 ± 0.08 m2 g−1 through N2 adsorption experiments and Brunauer–Emmett–Teller (BET) analysis. The Uv-vis absorption spectrum indicates that surface plasmon resonance (SPR) of silver nanostructure exists on the NPS samples, implying the potential application of NPS in surfaced enhanced Raman scattering (SERS)-active substrate, surface plasmon-based analytical devices, etc.

In the present paper, we have investigated the dealloying of Pt- and/or Pd-doped Al2Au intermetallic compounds and the formation of ultrafine nanoporous Au (np-Au) alloys through a chemical dealloying strategy. The microstructural characterization confirms that these doping atoms enter into crystal lattices of the precursors and then transmit into the as-obtained np-Au, both existing in the form of solid solutions. When dealloying in the 20 wt % NaOH solution is performed, a certain amount of Pt and/or Pd addition shows a superior refining effect and the ligament/channel sizes of the as-doped np-Au can be facilely modulated below 10 nm. When dealloying in the 5 wt % HCl solution is performed, however, the anticoarsening capacity of Pt doping is more remarkable compared with that of Pd doping. In addition, the amount of doping also has an important influence on the ligament resistance to coarsening. Apart from causing the refinement of ligaments/channels, the introduction of Pt and/or Pd into np-Au has generated novel bi- or trimetallic functionalized nanoporous alloys. These as-doped np-Au alloys with an appropriate amount of Pt and/or Pd exhibit excellent electrocatalytic activities toward methanol and formic acid oxidation and will find promising applications in the catalysis-related areas.

A novel electrocatalyst, nanoporous palladium (npPd) rods can be facilely fabricated by dealloying a binary Al80Pd20 alloy in a 5 wt.% HCl aqueous solution under free corrosion conditions. The microstructure of these nanoporous palladium rods has been characterized using scanning electron microscopy and transmission electron microscopy. The results show that each Pd rod is several microns in length and several hundred nanometers in diameter. Moreover, all the rods exhibit a typical three-dimensional bicontinuous interpenetrating ligament-channel structure with length scale of 15–20 nm. The electrochemical experiments demonstrate that these peculiar nanoporous palladium rods (mixed with Vulcan XC-72 carbon powders to form a npPd/C catalyst) reveal a superior electrocatalytic performance toward methanol oxidation in the alkaline media. In addition, the electrocatalytic activity obviously depends on the metal loading on the electrode and will reach to the highest level (223.52 mA mg−1) when applying 0.4 mg cm−2 metal loading on the electrode. Moreover, a competing adsorption mechanism should exist when performing methanol oxidation on the surface of npPd rods, and the electro-oxidation reaction is a diffusion-controlled electrochemical process. Due to the advantages of simplicity and high efficiency in the mass production, the npPd rods can act as a promising candidate for the anode catalyst for direct methanol fuel cells (DMFCs).

We show here that novel nanomaterials can be fabricated by an ancient casting technology. Titanium carbide (TiC) nanowires have been synthesized by casting NiTi alloys containing a little amount of carbon. The morphology and structure of the TiC nanowires have been investigated using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The TiC nanowires have a single crystalline structure and grow along the <100> direction. The diameters of the TiC nanowires range from 50 to 500 nm, and their lengths vary from 10 to 100 μm. Moreover, the diameters and lengths of the TiC nanowires can be adjusted by simply changing applied cooling rates during casting. The TiC nanowires have high aspect ratios of 80–500, which are beneficial to their field emission performance. A eutectic reaction mechanism has been presented to explain the formation of the TiC nanowires. The ancient casting technology may be used to synthesize novel nanowires of other metal carbides, oxides or nitrides. Our findings can provide implications for fabricating novel nanomaterials using ancient or traditional technologies.

The electrochemical dealloying of rapidly solidified Al-based alloys in a 1 M NaCl aqueous solution has been investigated using electrochemical measurements in combination with microstructural analysis. The results show that nanoporous metals (Au, Ag, Pd and Cu) with various morphologies can be fabricated through electrochemical dealloying of the Al-based alloys in the NaCl solution. The electrochemical behaviors of elemental metals (Al, Au, Ag, Pd and Cu) and precursor alloys for dealloying have been studied through open-circuit measurements, potentiodynamic anodic polarization and cyclic voltammetry. The dealloying mechanisms of the precursor alloys and the formation of the nanoporous metals have been analyzed based on cyclic voltammetry curves, chronoamperometry curves obtained at potentials above or below the critical potentials, and microstructural features of the as-dealloyed samples. In addition, a classification for dealloying of a bi-phasic alloy has been proposed according to different dealloying behaviors of coexistent phases in the alloy. It has been found that interactions between coexistent phases prevail during dealloying of the bi-phasic alloy and are in principle dependent on the diffusivity of the more noble element, the curvature-dependent undercritical potential dissolution, and the reaction between the more noble element and chloride ion.

An ultrafine nanoporous Ag80Pd20 alloy can be fabricated by chemical dealloying of a rapidly solidified Mg60Ag32Pd8 alloy. The addition of the third element Pd into Mg–Ag realizes the design and functionalization of a nanoporous bimetallic structure, which exhibits superior catalytic activity towards electro-oxidation of ethanol.

Effect of Ag or Pd additions on the microstructure, crystallization and thermal stability of Al85Ni10Ce5 amorphous alloys has been investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and differential scanning calorimetry (DSC). The results show that there are quenched-in nuclei in the Ag or Pd doped Al–Ni–Ce amorphous alloys, resulting in the formation of a shoulder peak on the XRD patterns. Moreover, the Pd doped Al–Ni–Ce amorphous alloys contain more and larger quenched-in nuclei than the Ag doped alloys. The Ag addition decreases the crystallization onset temperature, activation energy and thermal stability of the Al–Ni–Ce amorphous alloys, while the Pd addition greatly improves the crystallization onset temperature, activation energy and thermal stability of the amorphous alloys. The influence of the Ag or Pd additions on the crystallization and thermal stability of the Al–Ni–Ce amorphous alloys has been discussed based upon the existence of pre-existing quenched-in nuclei, chemical affinity between Al and additional elements, and diffusion of atoms.

We present a facile route to fabricate nanoporous gold composites (NPGCs) through chemical dealloying of two phase Al–Au alloys comprising Al2Au and AlAu intermetallic compounds under free corrosion conditions. The microstructures of the NPGCs were characterized using X-ray diffraction, scanning electron microscopy with energy dispersive X-ray analysis, and transmission electron microscopy. The dealloying of Al2Au and AlAu separately proceeds, and results in the formation of the NPGCs. The microstructures of the NPGCs are composed of intracellular and intercellular areas which exhibit two kinds of nanoporous structures with different length scales of ligaments/channels. The nanoporous structure of the intracellular areas forms due to the dealloying of Al2Au and that of the intercellular area forms owing to the dealloying of AlAu. Moreover, the proportion of the intercellular areas in the NPGCs increases with increasing Au content in the starting Al–Au alloys. In addition, the length scale of ligaments/channels in the NPGCs can be adjusted by simply changing the dealloying solution. The NPGCs show abnormal coarsening behaviors when subjected to annealing at different temperatures. In comparison to nanoporous gold (NPG) with a homogeneous structure, the NPGCs exhibit higher Young's modulus and yield strength. We can tailor the microstructures, properties and applications of these NPGCs through changing the composition of the starting Al–Au alloys, changing the dealloying solution, and adopting proper post treatment including annealing at high temperatures and acid treatment at room temperature.

Nanoporous gold (NPG) ribbons have been fabricated through electrochemical dealloying of melt-spun Al–Au alloys with 20–50 at.% Au in a 10 wt.% NaCl aqueous solution under potential control at room temperature. The microstructures of NPG were characterized using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray (EDX) analysis. The microstructures of the NPG ribbons strongly depend upon the phase constitutions of the starting Al–Au alloys. The single-phase Al2Au or AlAu intermetallic compound can be fully dealloyed, resulting in the formation of NPG with a homogeneous porous structure. The separate dealloying of Al2Au and AlAu in the two-phase Al–45 Au alloy leads to the formation of NPG composites (NPGCs). In addition, the dealloying of the Al–20 Au alloy comprising α-Al and Al2Au leads to the formation of NPG with bimodal channel size distributions. According to the ligament size, the surface diffusivity of Au adatoms along the alloy/electrolyte interface has been evaluated and increases with increasing applied potential. The dealloying mechanism in the neutral NaCl solution has been explained based upon pourbaix diagram and chloride ion effect.

A new Mg–Cu system has been developed to fabricate monolithic nanoporous copper (NPC) ribbons and bulk NPC through chemical dealloying in a 5 wt.% HCl solution. The microstructures of the NPC ribbons were characterized using X-ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis. The results show that the compositions of the melt-spun Mg–Cu alloys have an important effect on the dealloying process and microstructures of the NPC ribbons. Moreover, the synergetic dealloying of Mg2Cu and MgCu2 in two-phase Mg–Cu alloys results in the formation of NPC with a uniform porous structure.

Nanoporous palladium (NPPd) with ultrafine ligament size of 3–6 nm was fabricated by dealloying of an Al–Pd alloy in an alkaline solution. Electrochemical measurements indicate that NPPd exhibits significantly high electrochemical active specific surface area (23 m2 g−1), and high catalytic activity for electro-oxidation of methanol, ethanol, and formic acid. Mass activities can reach 149, 148, 262 mA mg−1 for the oxidation of methanol, ethanol and formic acid, respectively. Moreover, superior steady-state activities can be observed for all the electro-oxidation processes. NPPd will be a promising candidate for the anode catalyst for direct alcohol or formic acid fuel cells.

In this paper, the effect of alloy composition on the formation of porous Ni catalysts prepared by chemical dealloying of rapidly solidified Al–Ni alloys has been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis and N2 adsorption experiments. The experimental results show that rapid solidification and alloy composition have a significant effect on the phase constituent and microstructure of Al–Ni alloys. The melt spun Al–20 at.% Ni alloy consists of α-Al, NiAl3 and Ni2Al3, while the melt spun Al–25 and 31.5 at.% Ni alloys comprise NiAl3 and Ni2Al3. Moreover, the formation and microstructure of the porous Ni catalysts are dependent upon the composition of the melt spun Al–Ni alloys. The morphology and size of Ni particles in the Ni catalysts inherit from those of grains in the melt spun Al–Ni alloys. Rapid solidification can extend the alloy composition of Al–Ni alloys suitable for preparation of the Ni catalysts, and obviously accelerate the dealloying process of the Al–Ni alloys.

In this paper, the formation of nanocrystalline TiC from titanium powders and different carbon resources by mechanical alloying (MA) has been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The experimental results show that nanocrystalline TiC can be synthesized from Ti powders and different carbon resources (activated carbon, carbon fibres or carbon nanotubes) by MA at room temperature. Titanium and different carbon resources have a significant effect on the Ti–C reaction and the formation of TiC during MA. Moreover, the formation of nanocrystalline TiC is governed by a gradual diffusion reaction mechanism during MA, regardless of different carbon resources.

Nanoporous metal ribbons including Au, Pd, Pt, Ag, and Cu can be fabricated through chemical dealloying of rapidly solidified Al-based alloys under free corrosion conditions. The formation and microstructure of these nanoporous metals have been investigated using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, transmission electron microscopy, and high-resolution transmission electron microscopy. All metal ribbons exhibit an open, three-dimensional bicontinuous interpenetrating ligament-channel structure with nanometer length scales. For a given dealloying solution, the length scale of ligaments/channels in these nanoporous metals is associated with surface diffusion of more noble atoms, and increases with increasing diffusion coefficients in sequence: Pt/Pd < Au < Ag < Cu. In addition, the length scale of ligaments/channels of these nanoporous metals can be modulated by simply changing the dealloying solution. Nanoindentation tests show that Young’s modulus and hardness of nanoporous gold are dependent upon the length scale of ligaments/channels. The electrical resistivity of these nanoporous metals is one to two orders of magnitude higher than that of their bulk counterparts. These nanoporous metals can be good candidates to probe the mechanical, physical, and chemical properties associated with random porous structures of nanoporous solids and will find wide applications in catalysis, sensors, actuators, fuel cells, and so forth.

We present a facile and effective route to fabricate monolithic nanoporous silver (NPS) ribbons through chemical dealloying of melt-spun Al−Ag alloys comprising α-Al(Ag) and Ag2Al under free corrosion conditions. The microstructure of the NPS ribbons was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray analysis (EDX). The experimental results show that alloy composition and dealloying solution have a significant influence on the dealloying process and the formation of NPS. The Al−Ag alloys with 15−40 atom % Ag can be fully dealloyed in the 5 wt % HCl solution, but a minor amount of undealloyed Ag2Al can be detected in the as-dealloyed ribbons from the Al-45 and 50 Ag alloys. The existence of α-Al(Ag) can supply penetration paths for the solution and promote the dealloying of Ag2Al in the two-phase Al−Ag alloys. Moreover, the synergetic dealloying of α-Al(Ag) and Ag2Al in the two-phase Al−Ag alloys and fast surface diffusion of Ag result in the formation of NPS with a homogeneous porous structure. The Al−Ag alloys with 15−50 atom % Ag cannot be fully dealloyed in the 20 wt % NaOH solution, leading to the formation of NPS/Ag2Al composites. In addition, the Al-60 Ag alloy containing a single Ag2Al phase does not react with the 5 wt % HCl or 20 wt % NaOH solution even at high temperatures (90 ± 5 °C).

We present a novel and simple strategy to synthesize nanoporous gold (NPG) ribbons with bimodal channel size distributions. The NPG ribbons can be fabricated from Al−Au alloys through rapid solidification and chemical dealloying. The microstructure of these NPG ribbons was characterized using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, transmission electron microscopy, and high-resolution transmission electron microscopy. These NPG ribbons are composed of large-sized channels (hundreds of nanometers) with highly porous channel walls (tens of nanometers). Both large- and small-sized channels are 3D, open, and bicontinuous. The length scales of the large-sized channels can be modulated by changing the alloy composition, and those of small ligaments/channels in the channel walls can be tuned by changing the dealloying solution.

In the present work, phase transformations during mechanical alloying (MA) and post-MA annealing of Al70Cu20Fe10 have been investigated using X-ray diffraction (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). No icosahedral quasicrystalline phase (i-phase) is observed during the milling process of Al70Cu20Fe10. A totally disordered β-Al(Cu,Fe) phase firstly forms in the as-milled powders after 40 h of MA and thus transforms into the stable β-phase with a B2 structure with increasing milling time up to 70 h. The i-phase appears in the as-annealed products and its amount increases with increasing milling time. In addition, the ω-Al7Cu2Fe phase only forms after heat treatment of the milled Al70Cu20Fe10 powders. Furthermore, the formation of both the i-phase and ω-phase depends upon the milling time and annealing temperature.

In the present work, the microstructure of a melt-spun Al–10 Sb alloy has been characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that rapid solidification has no influence on the phase constitution of the Al–10 Sb alloy. Moreover, the phase constitution does not change with increasing quenching rate (wheel speed). However, rapid solidification has a significant effect on the microstructure of the Al–10 Sb alloy. The microstructure of the melt-spun Al–10 Sb alloy dominantly comprises equiaxed primary AlSb dendrites and nanoscale α-Al/AlSb eutectic, different from that of the ingot-cast alloy consisting of coarse primary AlSb plates within the α-Al/AlSb eutectic matrix. Some epitaxial orientation relationships were found between AlSb particles and α-Al matrix in the melt-spun Al–10 Sb alloy as follows: α-Al [3 1 0] ||AlSb [1 1 0] and α-Al (0 0 2) ||AlSb (2 2¯ 0).

In the present work, the effect of quenching rate (wheel speed) on the microstructure of a melt-spun Al–5Sb alloy has been investigated using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The phases were identified to be α-Al and AlSb in the alloy melt-spun at 500 and 1500 rpm. The microstructure of the alloy melt-spun at 500 rpm is composed of primary AlSb particles embedded in a matrix comprising equiaxed α-Al cells with intercellular nanoscale AlSb particles and α-Al/AlSb eutectic. Furthermore, intracellular nanoscale AlSb particles were also found in some areas. With increasing quenching rate to 1500 rpm, the matrix microstructure comprises elongated α-Al cells with intercellular nanoscale AlSb particles. The intercellular AlSb particles exhibiting intense Bragg reflections with monocrystalline characteristics possess the same crystallographic orientation but the intracellular ones are randomly oriented exhibiting spotty rings in the Al–5Sb alloy melt-spun at 500 rpm.

In the present work, microstructural evolution and microhardness of a melt-spun Al–5Ti–1B alloy during annealing have been investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM) together with energy dispersive spectroscopy (EDS) and hardness testing. The phases present in the as-annealed Al–5Ti–1B alloy were determined to be α-Al, the equilibrium tetragonal TiAl3 and hexagonal TiB2, whereas only α-Al and TiB2 were identified in the as-spun alloy. Most of Ti in the α-Al solid solution rapidly precipitates by annealing at 500 °C and the low diffusivity of Ti in Al suppresses the coarsening of the TiAl3 precipitates with prolonged annealing time. Age hardening effect is not observed in the melt-spun Al–5Ti–1B alloy. The microhardness sharply decreases by annealing at 500 °C for 5 min and then slightly changes with prolonged time to 60 min. The microhardness keeps unchanged by annealing at 200 °C for 60 min, while annealing at 300 °C or higher temperatures causes a continuous decrease in microhardness. The microhardness of the as-spun Al–5Ti–1B alloy appears to be governed by a combination of Hall–Petch hardening from the α-Al cell size and solid solution hardening of the α-Al matrix, whereas the microhardness of the as-annealed alloy is mainly governed by a combination of Hall–Petch hardening from the α-Al cell size and particle radius dependent Orowan hardening.

In the present work, the microstructure of melt-spun Al–10Ti–1C alloy has been characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The phases present in the melt-spun alloy are identified to be α-Al solid solution, the equilibrium tetragonal TiAl3 and hexagonal TiC by XRD and electron diffraction. Both large and small TiAl3 particles are observed in melt-spun Al–10Ti–1C alloy. The large TiAl3 particles, ∼1 μm in size, exhibit a homogeneous single-phase structure. The small TiAl3 particles are blocky, ∼0.1–0.2 μm in size. Some of them are a homogeneous single phase but some of them exhibit an ultrafine nanocellular structure. Polygonal TiC particles, ∼1.2–1.5 μm in size, are found in melt-spun Al–10Ti–1C alloy. Both TiAl3 and TiC particles are found to act as heterogeneous sites nucleating α-Al grains in the melt-spun alloy. The reasons for the formation of the microstructure of melt-spun Al–10Ti–1C alloy have also been discussed.

In the present work, the effect of the melt ejection temperature and peripheral wheel speed on the microstructure of melt-spun Al–20 Ce (wt.%) alloy was investigated using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Ejection temperature and wheel speed have no effect on the phase constitution, but have a marked effect on the microstructure of the melt-spun alloy. The phases present are identified to be the equilibrium α-Al and α-Al11Ce3. The microstructure of the alloy quenched from 1200 °C and at 1500 rpm is composed of α-Al dendrites and microdendrites with interdendritic α-Al11Ce3, while the microstructure of the alloy quenched from 900 °C and at 1500 rpm is predominantly comprised of α-Al microdendrites with interdendritic α-Al11Ce3. A variety of microstructures composed of aligned α-Al dendrites with interdendritic α-Al11Ce3, α-Al dendrites with interdendritic α-Al/α-Al11Ce3 eutectic and fully lamellar α-Al/a-Al11Ce3 eutectic are found in the Al–20 Ce alloy quenched from 1200 °C and at 500 rpm. Some orientation relationships were also determined.

In the present work, the microstructure of a melt-spun Al–5 Sb alloy has been characterized using X-ray diffraction and transmission electron microscopy. The phases present in the melt-spun Al–5 Sb alloy were determined to be the equilibrium α-Al and AlSb, identical to those in the ingot-cast alloy. The microstructure of the melt-spun Al–5 Sb alloy is composed of primary AlSb phase embedded in the matrix comprising α-Al cells with intercellular nanoscale AlSb particles, different from that of the ingot-cast alloy composed of the primary AlSb phase within an α-Al/AlSb eutectic matrix. Rapid solidification has a marked effect on the morphology, size and distribution of the primary AlSb phase in the melt-spun Al–5 Sb alloy. Furthermore, some orientation relationships were determined in the melt-spun alloy.

In this work, the microstructures of an Al–10 wt.% Sr alloy prepared by molten salts electrolysis and direct mixing method have been investigated using scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). It has been found that the microstructure of the deeply etched Al–10 wt.% Sr alloy prepared by electrolysis is markedly different from that prepared by direct mixing method. The primary Al4Sr phase is dendritic in the electrolysis-prepared Al–10 wt.% Sr alloy but slablike in the mixing-prepared alloy. The eutectic Al4Sr phase in the electrolysis-prepared alloy is much finer and more complex in morphology than that in the mixing-prepared alloy. It can be speculated that the intensive current and electromagnetic field in the electrolysis process have a significant effect on the liquid structure of the Al–Sr melt and the subsequent solidification process and the microstructure.

Preferred crystallographic orientations of primary Al4Sr dendrites in a rapidly solidified Al–23 Sr (wt.%) alloy have been investigated using transmission electron microscopy (TEM). The Al4Sr dendrites with 90° branches are dominant in the Al–23 Sr alloy melt-spun at 500 rpm and the dendrite orientation is the 〈110〉 direction. Wheel speed has a significant effect on the morphology and preferred orientation of the Al4Sr dendrites in the melt-spun Al–23 Sr alloy.

In the present work, the annealing-induced microstructural evolution of melt-spun Al–10% Sr (in wt.%) alloy has been investigated, using differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). A monotonically decreasing signal was observed on the DSC trace of the melt-spun Al–10% Sr alloy isothermally annealed at 600 °C, indicating that the microstructural evolution is a grain growth process rather than one of nucleation and growth. The nanoscale Al4Sr phase in as-quenched Al–10% Sr alloy grows with increasing annealing temperature and time. Furthermore, the Al4Sr particles are not randomly oriented and grow along a certain direction with respect to the Al matrix.

The electrochemical dealloying of rapidly solidified Al-based alloys in a 1 M NaCl aqueous solution has been investigated using electrochemical measurements in combination with microstructural analysis. The results show that nanoporous metals (Au, Ag, Pd and Cu) with various morphologies can be fabricated through electrochemical dealloying of the Al-based alloys in the NaCl solution. The electrochemical behaviors of elemental metals (Al, Au, Ag, Pd and Cu) and precursor alloys for dealloying have been studied through open-circuit measurements, potentiodynamic anodic polarization and cyclic voltammetry. The dealloying mechanisms of the precursor alloys and the formation of the nanoporous metals have been analyzed based on cyclic voltammetry curves, chronoamperometry curves obtained at potentials above or below the critical potentials, and microstructural features of the as-dealloyed samples. In addition, a classification for dealloying of a bi-phasic alloy has been proposed according to different dealloying behaviors of coexistent phases in the alloy. It has been found that interactions between coexistent phases prevail during dealloying of the bi-phasic alloy and are in principle dependent on the diffusivity of the more noble element, the curvature-dependent undercritical potential dissolution, and the reaction between the more noble element and chloride ion.

The surface stress–charge coefficient, ζ, is a fundamental material parameter and reflects the response of surface stress to the change of superficial charge. The sign and the quantity of ζ play a crucial role in electrochemically induced actuation of nanostructured metals. Here, for the first time, we address the electrochemical actuation and the associated stress–charge coefficients of bulk nanoporous nickel (np-Ni) in both strongly (NaOH) and weakly (NaF) adsorbed electrolytes. The results reveal a normal negative value of ζ for the np-Ni with the clean surface, and unusual positive values of ζ for the oxide-covered surface. Interestingly, the oxidized np-Ni cannot recover the conventional negative value of ζ even in the cathodic potential window. Moreover, the reversible strain amplitude and the involved charge are quite different in distinct potential windows (the same electrolyte) or in different electrolytes (strongly or weakly adsorbed). In addition, density functional theory (DFT) calculations have been performed to understand the electrochemical actuation behaviors of the np-Ni with different surface states. In some aspects, the scenario of the np-Ni indeed differs from that of nanoporous noble metals like Au or Pt. Our findings provide useful information on understanding the electrochemical actuation of nanostructured metals, and novel actuators or sensors could be developed based upon earth-abundant metals like Ni, Co, and so forth.

In the present study, magnetic nanoporous Cu(NPC)/(Fe,Cu)3O4 composites with tunable magnetism and excellent conductivity were fabricated by a facile one-step dealloying process. Three ternary Al–Cu–Fe alloys with different compositions were chosen as the precursors to carry out the dealloying process in a 20 wt% NaOH solution under free corrosion conditions. The microstructure of these NPC/(Fe,Cu)3O4 composites have been characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, transmission electron microscopy (TEM), and high resolution transmission electron microscopy (HRTEM) with nanobeam-EDX (NB-EDX). These NPC/(Fe,Cu)3O4 composites are composed of a NPC matrix with ligament/channel sizes of 20–40 nm and octahedral (Fe,Cu)3O4 embedded particles of 600–800 nm. The formation of these composites has been discussed based upon the surface diffusion of Cu adatoms and oxidation of Fe/Cu adatoms during dealloying. The N2 absorption/desorption results show that the NPC/(Fe,Cu)3O4 composites have a high surface area of up to 25.24 m2 g−1. The maximum values of the magnetic parameters of these NPC/(Fe,Cu)3O4 composites can reach 27.3 emu g−1, 7.7 emu g−1 and 218.5 Oe for the saturation magnetization, remanence and coercivity, respectively. The magnetic properties and the ratio of NPC:(Fe,Cu)3O4 in the NPC/(Fe,Cu)3O4 composites can be tuned by simply changing the Cu/Fe ratio in the Al–Cu–Fe precursor alloys, while keeping their excellent electrical conductivity. These functional composites will find potential applications in sensors, information storage, medical diagnostics, and so forth.

Metallic actuators (metallic muscles) have attracted a great deal of interest because of their potential advantages over piezoelectric ceramics and conducting polymers. However, to develop high performance actuators using earth's abundant and inexpensive metallic elements is a formidable challenge so far. Here, we report the design and fabrication of nickel-based actuators with low material cost (<1/2000 of gold), which demonstrate an unprecedented performance including giant reversible strain (up to 2%), ultrahigh work density (11.76 MJ m−3, the highest among the known actuator materials), and long cycle life (70% strain retention after 10000 cycles). This outstanding performance of the nickel-based actuators originates from their unique hierarchically nanoporous structure and the oxide-covered nature of the Ni surface.

Here, we report the fabrication of ultrafine nanoporous PdFe/Fe3O4 electrocatalysts by a facile dealloying strategy. The results show that the phase formation of the as-dealloyed samples is dependent upon the Pd:Fe atomic ratio in the Al–Pd–Fe ternary precursors. The size of ligaments is as small as ∼2 nm in the nanoporous structure of the as-dealloyed samples, which is the smallest among the literature data reported for nanoporous metals/alloys. The present nanoporous PdFe/Fe3O4 nanocomposites show excellent electrocatalytic activities towards the oxidation of methanol and ethanol in alkaline media due to the double enhancement from Fe3O4 and Fe in PdFe. In addition, the nanoporous PdFe/Fe3O4 sample dealloyed from the Al75Pd12.5Fe12.5 precursor exhibits the highest electrocatalytic activity. These materials are potential anode electrocatalysts for applications in direct alcohol fuel cells.

Rechargeable lithium ion batteries (LIBs) have transformed portable electronics and will play a crucial role in transportation, such as electric vehicles. For higher energy storage in LIBs, two issues should be addressed, that is, the fundamental understanding of the chemistry taking place in LIBs and the discovery of new materials. Here we design and fabricate two-dimensional (2D) WS2 nanosheets with preferential [001] orientation and perfect single crystalline structures. Being used as an anode for LIBs, the WS2-nanosheet electrode exhibits a high specific capacity, good cycling performance and excellent rate capability. Considering the controversy in the lithium storage mechanism of WS2, ex-situ X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS) analyses clearly verify that the recharge product (3.0 V vs. Li+/Li) of the WS2 electrode after fully discharging to 0.01 V (vs. Li+/Li) tends to reverse to WS2. More remarkably, the [001] preferentially-oriented 2D WS2 nanosheets are also promising candidates for applications in photocatalysis, water splitting, and so forth.

As promising electrode materials for electrochemical supercapacitors, pseudocapacitive transition metal oxides such as NiO possess high theoretical specific capacitance, environmental benignity and good abundance. However their areal capacitance and cycling stability are greatly restricted by their poor electronic conductivity (NiO, 10−2 to 10−3 S cm−1). Here we propose an in situ growth strategy in combination with nanoscale design to construct ultrathin mesoporous NiO nanosheets on a 3D network of nickel foam. The hybrid structures show well enhanced conductivity and ion transfer, giving rise to an ultrahigh specific capacitance of 2504.3 F g−1 which is close to the theoretical value of NiO. The electrodes also exhibit remarkable cycling stability (no degradation of the overall capacitance after 45000 cycles). The amazing electrochemical performance of such hybrid structures makes them potential electrodes in supercapacitors. The present strategy could be popularized in other transition metal oxides like Co3O4, MnO2, etc. to create electrodes with desirable nanostructures.

Nanostructured Cu oxides/hydroxides are promising materials for supercapacitors because of their high theoretical capacitance, low cost and friendliness to environment. However, the development of commercially viable Cu oxides/hydroxides with superior capacitive performance is still challenging. Here, 3D binder-free Cu2O@Cu nanoneedle arrays electrode was developed via facile electrochemistry. The electrode exhibits a high capacitance of 862.4 F g−1 and excellent cycling stability (20000 cycles). Furthermore, we have successfully constructed a Cu2O@Cu//AC asymmetric supercapacitor, which can achieve an energy density of 35.6 W h kg−1 at 0.9 kW kg−1 and excellent stability with a capacitance retention of 92% after 10000 cycles. After being charged for dozens of seconds, the in-series Cu2O@Cu//AC supercapacitors can light up LED arrays and even charge a mobile phone. These fascinating performances reasonably indicate their potential in commercial applications for energy storage.

Here we report the preparation of 3D binder-free NiO nanorod-anchored Ni foam electrodes, and their application as anode materials for rechargeable lithium-ion batteries. By anodization followed by thermal annealing, blooming flower-like NiO arrays were anchored to Ni foam, and were characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and N2 adsorption–desorption experiments. Electrochemical properties were evaluated by cyclic voltammetry (CV) and galvanostatic cycling. Cycling performance shows that after 70 cycles the NiO nanorod-anchored Ni foam electrode can still deliver a stable reversible capacity up to 705.5 mA h g−1 and 548.1 mA h g−1 with a high coulombic efficiency (≥98%) at a constant current density of 1 A g−1 and 2 A g−1, respectively. The superior performance of the NiO electrode can be attributed to its favorable morphology and the excellent electrical contact between NiO and the current collector of Ni foam. The present strategy can be extended to fabricate other self-supported transition metal oxide nanostructures for high-performance lithium-ion batteries.

Here we report a facile efficient anodization approach to fabricate nickel oxalate nanostructures on nickel foam (NON@NF). The NON@NF electrode exhibits high specific capacitance and excellent cycling performance. Moreover, an assembled asymmetric supercapacitor based upon NON@NF and activated carbon shows excellent performance with high energy/power density and long cycling stability.

We present a facile route to fabricate nanoporous gold composites (NPGCs) through chemical dealloying of two phase Al–Au alloys comprising Al2Au and AlAu intermetallic compounds under free corrosion conditions. The microstructures of the NPGCs were characterized using X-ray diffraction, scanning electron microscopy with energy dispersive X-ray analysis, and transmission electron microscopy. The dealloying of Al2Au and AlAu separately proceeds, and results in the formation of the NPGCs. The microstructures of the NPGCs are composed of intracellular and intercellular areas which exhibit two kinds of nanoporous structures with different length scales of ligaments/channels. The nanoporous structure of the intracellular areas forms due to the dealloying of Al2Au and that of the intercellular area forms owing to the dealloying of AlAu. Moreover, the proportion of the intercellular areas in the NPGCs increases with increasing Au content in the starting Al–Au alloys. In addition, the length scale of ligaments/channels in the NPGCs can be adjusted by simply changing the dealloying solution. The NPGCs show abnormal coarsening behaviors when subjected to annealing at different temperatures. In comparison to nanoporous gold (NPG) with a homogeneous structure, the NPGCs exhibit higher Young's modulus and yield strength. We can tailor the microstructures, properties and applications of these NPGCs through changing the composition of the starting Al–Au alloys, changing the dealloying solution, and adopting proper post treatment including annealing at high temperatures and acid treatment at room temperature.

Pt-based electrocatalysts play a crucial role in both the anode and cathode reactions of direct methanol fuel cells (DMFCs), but their activity/durability and cost are still the main issues to be addressed. Through the combination of mechanical alloying with dealloying, here we have fabricated a nanoporous PtCuTi (np-PtCuTi) alloy with a low Pt content from a Cu-based precursor. The np-PtCuTi alloy exhibits a three-dimensional bi-continuous interpenetrating ligament/channel structure with a ligament size of 3.1 ± 0.6 nm. Electrochemical measurements show that the np-PtCuTi alloy exhibits superior electrocatalytic activities (CO tolerance, specific and mass activity) towards methanol oxidation at the anode, compared to commercial PtC catalysts. Moreover, the np-PtCuTi catalyst shows an enhancement of 1.9 and 4.2 times in the mass and specific activity towards the oxygen reduction reaction (ORR) at the cathode compared to PtC, respectively. More importantly, the np-PtCuTi catalyst shows excellent catalytic durability for the ORR, and the mass activity retains 91.8% of the initial value after 20000 cycles. In addition, the mechanisms for the activity enhancement of np-PtCuTi have been rationalized on the basis of the structural effect, alloying effect and electronic effect through experiments and density functional theory calculations.