Active materials and special structures of the electrode have decisive influence on the electrochemical properties of supercapacitors. Herein, three-dimensional (3D) hierarchical NixCo1–xO/NiyCo2–yP@C (denoted as NiCoOP@C) hybrids have been successfully prepared by a phosphorization treatment of hierarchical NixCo1–xO@C grown on nickel foam. The resulting NiCoOP@C hybrids exhibit an outstanding specific capacitance and cycle performance because they couple the merits of the superior cycling stability of NixCo1–xO, the high specific capacitance of NiyCo2–yP, the mechanical stability of carbon layer, and the 3D hierarchical structure. The specific capacitance of 2638 F g–1 can be obtained at the current density of 1 A g–1, and even at the current density of 20 A g–1, the NiCoOP@C electrode still possesses a specific capacitance of 1144 F g–1. After 3000 cycles at 10 A g–1, 84% of the initial specific capacitance is still remained. In addition, an asymmetric ultracapacitor (ASC) is assembled through using NiCoOP@C hybrids as anode and activated carbon as cathode. The as-prepared ASC obtains a maximum energy density of 39.4 Wh kg–1 at a power density of 394 W kg–1 and still holds 21 Wh kg–1 at 7500 W kg–1.Keywords: carbon coverage; excellent performance; nickel cobalt oxide; nickel cobalt phosphide; supercapacitor;

Owing to unique optical, electronic, and catalytic properties, MoS2 have received increasing interest in electrochemical water splitting. Herein, few-layered Mo(1–x)WxS2 hollow nanospheres-modified Ni3S2 heterostructures are prepared through a facile hydrothermal method to further enhance the electrocatalytic performance of MoS2. The doping of W element optimizes the electronic structure of MoS2@Ni3S2 thus improving the conductivity and charge-transfer ability of MoS2@Ni3S2. In addition, benefitting from the few-layered hollow structure of Mo(1–x)WxS2, the strong electronic interactions between Mo(1–x)WxS2 and Ni3S2 and the hierarchical structure of one-dimensional nanorods and three-dimensional Ni foam, massive active sites and fast ion and charge transportation are obtained. As a result, the optimized Mo(1–x)WxS2@Ni3S2 heterostructure (Mo-W-S-2@Ni3S2) achieves an extremely low overpotential of 98 mV for hydrogen evolution reaction and 285 mV for oxygen evolution reaction at 10 mA cm–2 in alkaline electrolyte. Particularly, using Mo-W-S-2@Ni3S2 heterostructure as a bifunctional electrocatalyst, a cell voltage of 1.62 V is required to deliver a 10 mA cm–2 water splitting current density. In addition, the electrode can be maintained at 10 mA cm–2 for at least 50 h, indicating the excellent stability of Mo-W-S-2@Ni3S2 heterostructure. Therefore, this development demonstrates an effective and feasible strategy to prepare highly efficient bifunctional electrocatalysts for overall water splitting.Keywords: bifunctional electrocatalysts; few-layered; MoS2@Ni3S2; W-doping; water splitting;

Transition-metal sulfides have attracted extensive interest as oxygen evolution reaction (OER) catalyst alternatives to noble metal based catalysts but generally exhibit limited electrocatalytic activity. We here report hierarchical porous Fe3O4/Co3S4 composite nanosheets for a highly efficient electrocatalytic OER in alkaline electrolytes. The preparation of the composite involves a hydrothermal synthesis and a subsequent sulfurization process. The prepared porous Fe3O4/Co3S4 composite shows strong synergetic coupling effects, facilitating active site exposure, and facile charge transfer. Remarkably, Fe3O4/Co3S4 nanosheets afforded an electrocatalytic OER with a current density of 10 mA cm−2 at a low potential of 1.50 V and a small Tafel slope of about 56 mV dec−1. This indicates that the composite of porous Fe3O4/Co3S4 nanosheets is promising as an efficient electrocatalyst for the OER that can be used in the fields of fuel cells, metal-air batteries and water splitting for hydrogen production.

A series of Ni0.37Co0.63S2-reduced graphene oxide nanocomposites with different graphene contents (NCS@rGO-x) has been successfully prepared via a facile one-step hydrothermal method and applied as the catalysts for the oxygen evolution reaction (OER) and degradation of organic pollutants. The XRD and FESEM analyses revealed that the phase structure and morphology of NCS nanoparticles were substantially influenced by the graphene contents. The phase structure of NCS nanoparticles gradually transformed from primary NiCo2S4 to Ni0.37Co0.63S2 and the morphology and size of NCS nanoparticles were found to become more regular and homogeneous with the increase of graphene concentration. On the NCS@rGO-x nanocomposites, the NCS@rGO-2 sample demonstrated the best catalytic activity toward the OER, which delivers a stable current density of 10 mA cm−2 at a small overpotential of ∼276 mV (vs. RHE) with a Tafel slope as low as 48 mV dec−1. Furthermore, the NCS@rGO-2 sample showed the remarkable photocatalytic activity for degradation of methylene blue (MB), which may be attributed to the increased reaction sites and high separation efficiency of photogenerated charge carries due to the electronic interaction between NCS nanoparticles and rGO. All these impressive performances indicate that the NCS@rGO-2 nanocomposite is a promising catalyst in energy and environmental fields.

Recently, transition metal-based nanomaterials have played a key role in the applications of supercapacitors. In this study, nickel phosphide (Ni-P) was simply combined with NiCo LDH via facile phosphorization of Ni foam and subsequent electrodeposition to form core–shell nanorod arrays on the Ni foam; the Ni-P@NiCo LDH was then directly used for a pseudocapacitive electrode. Owing to the splendid synergistic effect between Ni-P and NiCo LDH nanosheets as well as the hierarchical structure of 1D nanorods, 2D nanosheets, and 3D Ni foam, the hybrid electrode exhibited significantly enhanced electrochemical performances. The Ni-P@NiCo LDH electrode showed a high specific capacitance of 12.9 F cm−2 at 5 mA cm−2 (3470.5 F g−1 at a current density of 1.3 A g−1) that remained as high as 6.4 F cm−2 at a high current density of 100 mA cm−2 (1700 F g−1 at 27 A g−1) and excellent cycling stability (96% capacity retention after 10 000 cycles at 40 mA cm−2). Furthermore, the asymmetric supercapacitors (ASCs) were assembled using Ni-P@NiCo LDH as a positive electrode and activated carbon (AC) as a negative electrode. The obtained ASCs delivered remarkable energy density and power density as well as good cycling performance. The enhanced electrochemical activities open a new avenue for the development of supercapacitors.

The electrochemical splitting of water, as an efficient and large-scale method to produce H2, is still hindered by the sluggish kinetics of the oxygen evolution reaction (OER) at the anode. Considering the synergetic effect of the different metal sites with coordination on the surface of electrocatalysts, the hybrids of Co/Fe phosphides (denoted as Co-Fe-P) is prepared by one-step phosphorization of CoFe metal–organic frameworks for the first time as highly efficient electrocatalysts for OER. Benefiting from the synergistic effect of Co and Fe, the high valence of Co ions induced by strongly electronegative P and N and the large electrochemical active surface area (ECSA) originated from exposed nanowires on the surface of Co/Fe phosphides, the resultant Co-Fe-P-1.7 exhibits remarkable electrocatalytic performances for OER in 1.0 M KOH, affording an overpotential as low as 244 mV at a current density of 10 mA/cm2, a small Tafel slope of 58 mV/dec, and good stability, which is superior to that of the state-of-the-art OER electrocatalysts. In addition, the two-electrode cell with Co-Fe-P-1.7 modified Ni foam as anode and cathode in an alkaline electrolyte, respectively, exhibits the decomposition potential of ca. 1.60 V at a current density of 10 mA/cm2 and excellent stability.Keywords: bimetal−organic frameworks; HER; OER; phosphides; water splitting;

There is a growing need for the electrode with high mass loading of active materials, where both high energy and high power densities are required, in current and near-future applications of supercapacitor. Here, an ultrathin Co3S4 nanosheet decorated electrode (denoted as Co3S4/NF) with mass loading of 6 mg cm−2 is successfully fabricated by using highly dispersive Co3O4 nanowires on Ni foam (NF) as template. The nanosheets contained lots of about 3∼5 nm micropores benefiting for the electrochemical reaction and assembled into a three-dimensional, honeycomb-like network with 0.5∼1 μm mesopore structure for promoting specific surface area of electrode. The improved electrochemical performance was achieved, including an excellent cycliability of 10,000 cycles at 10 A g−1 and large specific capacitances of 2415 and 1152 F g−1 at 1 and 20 A g−1, respectively. Impressively, the asymmetric supercapacitor assembled with the activated carbon (AC) and Co3S4/NF electrode exhibits a high energy density of 79 Wh kg−1 at a power density of 151 W kg−1, a high power density of 3000 W kg−1 at energy density of 30 Wh kg−1 and 73 % retention of the initial capacitance after 10,000 charge-discharge cycles at 2 A g−1. More importantly, the formation process of the ultrathin Co3S4 nanosheets upon reaction time is investigated, which is benefited from the gradual infiltration of sulfide ions and the template function of ultrafine Co3O4 nanowires in the anion-exchange reaction.

Ni0.31Co0.69S2 nanoparticle/reduced graphene oxide (Ni0.31Co0.69S2/rGO) composites have been synthesized via hydrothermal method, and then applied as the active materials for a high-performance non-enzymatic glucose sensor. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) were employed to characterize the morphology of the as-prepared samples. The results revealed that the abundant nanoparticles with the size of about 150 nm uniformly anchored on the reduced graphene oxide nanosheets, which are interconnected to form a porous graphene framework. The subsequent electrochemical measurements and kinetic analysis showed that the Ni0.31Co0.69S2/rGO composites possessed excellent electrocatalytic activity to glucose oxidation with a low detection limit of 0.078 μM and wide linear ranges of 0.001–5 mM and 5–16 mM. Moreover, the sensitivities for two linear ranges are 1753 μA mM−1 cm−2 and 954.7 μA mM−1 cm−2, respectively. In addition, the favorable selectivity, long-term stability and superior practical application were also obtained. All these results indicate that the Ni0.31Co0.69S2/rGO composites are a promising active material for non-enzymatic glucose sensors.

A novel photoelectrochemical (PEC) biosensing platform was constructed based on a ternary hybrid Ni/CdS/TiO2 nanotube array electrode, which was fabricated by the combination of electrochemical anodization and electrodeposition. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) confirmed that the CdS and Ni nanoparticles were homogeneously dispersed on the TiO2 nanotube arrays. Here, the Ni nanoparticles on the surface of CdS/TiO2 heterojunctions play a dual role in enhancing the performance of the PEC biosensor. First, Ni nanoparticles serve as a hole receptor, which can promote the fast charge separation and act as a protective layer that improves the stability of the Ni/CdS/TiO2 electrode. Second, Ni can remarkably improve the photoelectrochemical performance because it is a highly efficient electrocatalyst. As a result, the Ni/CdS/TiO2 nanotube array electrode offered much enhanced photocurrent compared to the CdS/TiO2 nanotube array electrode. Using glucose as a model, a highly sensitive photoelectrochemical biosensor based on the Ni/CdS/TiO2 nanotube array electrode was developed. Under optimized conditions, the biosensor displayed a wide linear range, a low detection limit as well as high selectivity and good stability. All these results indicate that this novel electrode is a promising candidate for use as a photoelectrochemical biosensor.

In this study, a good core–shell heterostructure of Pt NPs@UiO-66 was fabricated by encapsulating presynthesized platinum nanoparticles (Pt NPs) into the host matrix of UiO-66 which possesses the slender triangular windows with a diameter of 6 Å. The transmission electron microscopy images exhibited that the number of the encapsulated Pt NPs and the crystalline morphology of as-synthesized core–shell heterostructure samples had a series of changes with increasing the volume of the injected Pt NPs precursor solution. Among these samples, the Pt NPs@UiO-66-2 sample had a good crystalline morphology with several well-dispersed Pt NPs encapsulated in UiO-66 frameworks. But there were no obvious Pt NPs observed in the Pt NPs@UiO-66-1 sample, and for the Pt NPs@UiO-66-3 sample, the number of Pt NPs encapsulated in UiO-66 matrix notably reduced and the metal organic framework (MOF) crystals became small and aggregated. The electrochemical measurements showed that the Pt NPs@UiO-66-2 sample modified glass carbon electrode (GCE) presented a remarkable electrocatalytic activity toward hydrogen peroxide (H2O2) oxidation, including an excellent anti-interference performance even if the concentration of the interference species was the same as the H2O2, an extended linear range from 5 μM to 14.75 mM, a low detection limit, as well as good stability and reproducibility. The results indicate the superiority of MOFs in H2O2 detection. And more importantly, it will provide a new opportunity to promote the anti-interference performance of the nonenzyme electrochemical sensors.

In this work, three dimensional (3D) NixCo1−xS2/graphene composite hydrogels with different Ni contents (denoted as NixCo1−xS2/GH (x = 0, 0.31, 0.56, 0.66, 1)) have been synthesized by a simple one-step hydrothermal method and utilized as the active materials of supercapacitors. The as-prepared samples present a 3D interconnected porous network with the pore sizes in the range of several to tens micrometers. Interestingly, the NixCo1−xS2 particles are uniformly located on the graphene network and the particle size is evolved from ∼50 nm to ∼1.5 μm with the increase of Ni content. The electrochemical measurements revealed that the specific capacitance, rate capability and cyclability of different NixCo1−xS2/GH electrodes are strongly affected by their different Ni content. Among these, the 3D Ni0.31Co0.69S2/GH composite has the highest specific capacitance of 1166 F/g at a current density of 1 A/g. Furthermore, a specific capacitance of 559 F/g can be still maintained at high current density of 20 A/g. After 1000 charge–discharge cycles at 5 A/g, the specific capacitance remains a high value of 755 F/g.

•Cu–Ag superstructure was successfully prepared using the nature leaves as reductant.•The Cu–Ag/NF sensor displays a fascinating sensitivity for glucose oxidation.•The Cu–Ag/NF sensor shows good electrochemical properties towards glucose detection.•The Cu–Ag/NF sensor can be used for real sample with good accuracy and precision.Bimetallic Cu–Ag superstructures were successfully fabricated for the first time by using the natural leaves as reducing agent through a facile one-step hydrothermal process. Morphology, structure and composition of the Cu–Ag superstructures were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectra (XPS) and inductively coupled plasma-optical emission spectroscopy (ICP-OES), respectively. The results reveal that the Cu–Ag superstructure is bimetallic nanocomposite constructed by nanoparticles with low Ag content and shows a rough surface and porous flexural algae-like microstructure. By using a three-dimensional nickel foam as the scaffold, a novel non-enzymatic glucose sensor based on Cu–Ag nanocomposites has been fabricated and applied to non-enzymatic glucose detection. The as-prepared Cu–Ag nanocomposites based glucose sensor displays distinctly enhanced electrocatalytic activity compared to those obtained with pure Cu nanomaterials prepared with a similar procedure, revealing a synergistic effect of the matrix Cu and the doped Ag. Cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy indicate that the Cu–Ag superstructures based glucose sensor displays a fascinating sensitivity up to 7745.7 μA mM−1 cm−2, outstanding detection limit of 0.08 μM and fast amperometric response (<2 s) for glucose detection. Furthermore, the sensor also exhibits significant selectivity, excellent stability and reproducibility, as well as attractive feasibility for real sample analysis. Because of its excellent electrochemical performance, low cost and easy preparation, this novel electrode material is a promising candidate in the development of non-enzymatic glucose sensor.

3D Ni3S2 nanosheet arrays grown on Ni foam were successfully synthesized through a facile one-step hydrothermal approach and then directly applied as the electrode for a high-performance supercapacitor and non-enzymatic glucose sensor. The structure and morphology of the prepared Ni3S2 were characterized by X-ray power diffraction (XRD), field emission scanning electronic microscopy (FESEM) and transmission electron microscopy (TEM). The subsequent electrochemical measurements showed that the Ni3S2 nanosheet array electrode possessed a superior specific capacitance of 1370.4 F g−1 at a current density of 2 A g−1. Remarkably, a specific capacitance of 952.0 F g−1 could be still achieved at a high current density of 20 A g−1, indicating its excellent rate capability. And 91.4% of the specific capacitance was retained after 1000 cycles at a current density of 6 A g−1. Besides, to demonstrate its practical application, an asymmetric supercapacitor based on the Ni3S2 nanosheet array electrode as the positive electrode and activated carbon as the negative electrode was assembled. It delivered high energy density and good long-term stability. Additionally, serving as a non-enzymatic sensor, the 3D Ni3S2 nanosheet array electrode exhibited remarkable electrocatalytic activity towards glucose oxidation with a high sensitivity of 6148.0 μA mM−1 cm−2. All these impressive performances suggest that the Ni3S2 nanosheet array is a promising electrode material for supercapacitors and non-enzymatic glucose sensors.

In this work, a Ni/CdS bifunctional Ti@TiO2 core–shell nanowire electrode with excellent electrochemical sensing property was successfully constructed through a hydrothermal and electrodeposition method. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) were employed to confirm the synthesis and characterize the morphology of the as-prepared samples. The results revealed that the CdS layer between Ni and TiO2 plays an important role in the uniform nucleation and the following growth of highly dispersive Ni nanoparticle on the Ti@TiO2 core–shell nanowire surface. The bifunctional nanostructured electrode was applied to construct an electrochemical nonenzymatic sensor for the reliable detection of glucose. Under optimized conditions, this nonenzymatic glucose sensor displayed a high sensitivity up to 1136.67 μA mM–1 cm–2, a wider liner range of 0.005–12 mM, and a lower detection limit of 0.35 μM for glucose oxidation. The high dispersity of Ni nanoparticles, combined with the anti-poisoning faculty against the intermediate derived from the self-cleaning ability of CdS under the photoexcitation, was considered to be responsible for these enhanced electrochemical performances. Importantly, favorable reproducibility and long-term performance were also obtained thanks to the robust frameworks. All these results indicate this novel electrode is a promising candidate for nonenzymatic glucose sensing.

In this work, reticular-vein-like Cu@Cu2O/rGO nanocomposites have been synthesized by direct redox reaction of Cu and graphene oxide (GO) through a hydrothermal method where the macropore Cu sheets served as the precursor of reticular-vein-like Cu2O as well as the reducing agent of GO. FESEM and TEM were employed to characterize the morphology of the as-prepared samples. The results reveal that the reticular-vein-like Cu@Cu2O nanocomposites are homogeneously anchored onto rGO and act like the skeleton supporting the rGO sheets to avoid its aggregation or stacking. Electrochemical tests show that the Cu@Cu2O/rGO modified glassy carbon electrode (GCE) exhibits remarkable electrocatalytic activity towards glucose oxidation in both alkaline medium and human serum, including a wide linear range (0.005–7 mM), a low detection limit (0.5 μM), a rapid response (<2 s) as well as good stability and repeatability. More importantly, the interference from the commonly interfering species such as lactose, fructose, ascorbic acid (AA) and uric acid (UA) can be effectively avoided. All these results indicate this novel nanostructured material is a promising candidate for non-enzymatic glucose sensors.

3D NiχCo1−χ oxides with different morphologies for high-capacity supercapacitors were controllably synthesized via an electrodeposition method combined with a simple post annealing process. The synthesis involves the co-electrodeposition of the bimetallic (Ni, Co) hydroxide precursor on a nickel foam scaffold and subsequent thermal transformation to NiχCo1−χ oxides. The crystalline structure, morphology and electrochemical performance of the 3D NiχCo1−χ oxides can be readily manipulated by simply varying the Co/Ni molar ratio in the electrodeposition electrolyte. With the increase of the Co/Ni molar ratio, the characteristic peak intensities and the signal sites were gradually changed from a NiO crystal dominant structure to NiCo2O4 and finally to a Co3O4 dominant structure. Moreover, the morphology also can be controlled by adjusting the Co/Ni molar ratio in the electrodeposition electrolyte. In addition, the Ni0.61Co0.39 oxide electrode shows a large specific capacitance of 1523.0 F g−1 at 2 A g−1 and 95.30% of that can be retained, even at a high current density of 30 A g−1. The superior rate capability should be attributed to the unique 3D network-like architecture, which can enlarge the liquid–solid interfacial area, facilitate the electron and ion transport, and further increase the utilization of the active material. To demonstrate its practical application, an asymmetric supercapacitor based on the Ni0.61Co0.39 oxide electrode as a positive electrode and activated carbon as a negative electrode was fabricated. Owing to the outstanding capacitive behavior of the Ni0.61Co0.39 oxide electrode, the asymmetric device delivers a prominent energy density of 36.46 W h kg−1 at a power density of 142 W kg−1, and which holds great promise for potential applications in energy storage.

Three dimensional manganese dioxide/Pt/nickel foam (shortened to MnPtNF) hybrid electrodes were prepared by double-pulse polarization and potentiostatic deposition technologies for supercapacitor applications. The decoration of Pt nanoparticles onto nickel foam varies the nucleation mechanism of the manganese dioxide species, inducing the formation of manganese dioxide nanosheets. Additionally, controlling the size of the Pt nanoparticles leads to modulated nanosheet architecture and electrochemical properties of the manganese dioxide electrode, as revealed by XRD, Raman spectra, SEM, TEM, cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy. The nanosheet architecture of the MnPtNF electrode favors the transportation of electrons and ions, which results in the enhanced electrochemical properties. Importantly, the optimized MnPtNF electrode obtains a maximum specific capacitance of 1222 F g−1 at 5 A g−1 (89% of the theoretical specific capacitance of MnO2) and 600 F g−1 at 100 A g−1. Moreover, the presence of Pt nanoparticles in the MnO2 electrode effectively improves its cycling stability, which is confirmed by the increase of the specific capacitance retention from 14.7% to 90% after 600 cycles.

A class of novel composite electrodes based on poly(3,4-ethylenedioxythiophene) (PEDOT) and manganese dioxide (MnO2) was assembled by step-by-step anodic deposition on nickel foam for supercapacitor application. The effect of the distribution and loading of PEDOT on the electrochemical performance of composite electrodes was studied carefully. Among these composite electrodes, the optimized PEDOT/MnO2/PEDOT sandwich electrode shows excellent capacitive behavior, and MnO2 species in the optimized sandwich electrode possesses a high specific capacitance of 487.5 F g−1 at 1 A g−1. Furthermore, an asymmetric supercapacitor cell with the optimized sandwich composite as positive electrode and active carbon (AC) as negative electrode also exhibits outstanding performance at a cell voltage of 1.8 V in a 0.5 M Na2SO4 aqueous electrolyte. It has a high energy density of 30.2 Wh kg−1 with a power density of 180 W kg−1. And even at a high power density of 2.7 kW kg−1, the asymmetric supercapacitor can deliver a high energy density of 13.1 Wh kg−1. Moreover, the asymmetric supercapacitor displays impressive electrochemical cycling stability with 99.5% initial capacitance remained after 1000 continuous cycles.Graphical abstractHighlights► A class of PEDOT/MnO2 composite electrodes was prepared by anodic deposition. ► We employed SEM, TEM, Raman spectra and electrochemical tests. ► The impact of PEDOT distribution and loading on electrochemical property was studied. ► The optimized PEDOT/MnO2/PEDOT electrode possesses the best electrochemical properties.

Co3O4 microspheres with free-standing or bundled nanofibers (NFs) were fabricated for use as a platform for non-enzymatic glucose sensing. The sensor based on free-standing Co3O4 NFs displays enhanced sensitivity (1440 μA mM−1 cm−2), a wider linear range (0.005–12 mM) and superior selectivity. The application of this glucose sensor in human blood serum has also been demonstrated successfully.

A three dimensional (3D) nanostructured nickel oxide (NiO) electrode was fabricated by an electrodeposition method employing nickel foam (NF) as a scaffold and used for glucose detection. Taking advantage of the synergetic effect of NF and NiO, the 3D NiO/NF electrode shows excellent performance in glucose detection.

The effect of the electrodeposition temperature on the electrochemical performance of Ni(OH)2 electrode was investigated in this report. Ni(OH)2 was electrodeposited directly on nickel foam at different temperatures. The crystalline structure, morphology and specific surface area of the prepared Ni(OH)2 were characterized by X-ray powder diffraction (XRD), field emission scanning electronic microscopy (FESEM) and Brunauer–Emmett–Teller (BET). Electrochemical techniques such as cyclic voltammetry (CV), chronopotentiometry, and electrochemical impedance spectra (EIS) were carried out to systematically study the electrochemical performance of various Ni(OH)2 electrodes in 1 M KOH electrolyte. The results demonstrated that the electrodeposition temperature had obviously affected the properties of the Ni(OH)2. A pure α-Ni(OH)2 phase could be observed at low temperature. When the temperature increased to 65 °C, the β-Ni(OH)2 phase together with α-Ni(OH)2 phase were present. Moreover, the sample synthesized at 65 °C possessed a porous honeycomb-like microstructure and the corresponding specific capacitance was up to 3357 F g−1 at a charge–discharge current density of 4 A g−1, which suggested its potential application as an electrode material for supercapacitors.

A novel MnO2/graphene (G)/nickel foam (NF) composite as supercapacitor electrode was fabricated by a facile electrochemical deposition approach for the first time. The approach includes electrophoretic deposition of G on NF (EPD-G/NF) and electrodeposition of MnO2 on EPD-G/NF (MnO2/EPD-G/NF). Compared with other methods for preparing MnO2/G composite, our green strategy avoids using harsh chemicals (e.g. hydrazine) or high temperature treatment for reducing graphene oxide. Owing to unique structure, specific capacitance (Cs) of the MnO2/EPD-G/NF electrode is as high as 476 F g− 1 at high current density of 1 A g− 1 in 0.5 M Na2SO4 solution, which is the highest Cs for MnO2/G composites to date, and the Cs is higher than that of MnO2/NF electrode. Furthermore, it also exhibits high rate capacity, such as 216 F g− 1 of Cs at 10 A g− 1. On the other hand, our strategy provides a versatile method for fabrication of other G-based composites with metal oxide/hydroxide or conducting polymer as supercapacitor electrode.Graphical abstractHighlights► MnO2/graphene (G)/nickel foam composite was fabricated for the first time. ► The composite possesses unique porous structure. ► The composite shows the highest specific capacitance for MnO2/G composites to date. ► The composite exhibits high rate capacity (476 F g− 1 at 1 A g− 1, 216 F g− 1 at 10 A g− 1). ► Our strategy provides a versatile method for fabrication of other G-based composites.

The manganese oxide (MnO2) nanowires and cobalt hydroxide (Co(OH)2) nanosheets are successfully electrodeposited on nickel foam (NF), respectively (referred to as MnO2/NF and Co(OH)2/NF electrode hereinafter). Both electrodes show higher specific capacitance (Cs) and more excellent rate performance than that of most reported corresponding materials. In addition, our previous study of Ni(OH)2/NF electrodes also exhibited conspicuous results. Combined with the outstanding properties of NF, it is noticeable that the NF electrodes may be a promising choice for supercapacitors.

To improve the performance of direct ethanol fuel cells (DEFCs), a three-dimensional (3D), hierarchically structured Pd electrode has been successfully fabricated by directly electrodepositing Pd nanoparticles on the nickel foam (referred as Pd/Nickel foam electrode hereinafter). The electrochemical properties of the as-prepared electrode for ethanol oxidation have been investigated by cyclic voltammetry (CV). The results show that the oxidation peak current density of the Pd/Nickel foam electrode is 107.7 mA cm−2, above 8 times than that of Pd film electrode at the same Pd loading (0.11 mg cm−2), and a 90 mV negative shift of the onset potential is found on the Pd/Nickel foam electrode compared with the Pd film electrode. Furthermore, the peak current density of the 500th cycle remains 98.1% of the maximum value for the Pd/Nickel foam electrode after a 500-cycle test, whereas it is only 14.2% for the Pd film. The improved electrocatalytic activity and excellent stability of the Pd/Nickel foam electrode make it a favorable platform for direct ethanol fuel cell applications.

Mesoporous MnO2 nanowire array architecture exhibits enhanced capacitive and charge/discharge performance for electrochemical capacitors.

Electrodeposited Ni(OH)2 on nickel foam with porous and 3D nanostructures has ultrahigh capacitance in the potential range −0.05–0.45 V, and a maximum specific capacitance as high as 3152 F g−1 can be achieved in 3% KOH solution at a charge/discharge current density of 4 A g−1.

Ni0.31Co0.69S2 nanoparticle/reduced graphene oxide (Ni0.31Co0.69S2/rGO) composites have been synthesized via hydrothermal method, and then applied as the active materials for a high-performance non-enzymatic glucose sensor. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) were employed to characterize the morphology of the as-prepared samples. The results revealed that the abundant nanoparticles with the size of about 150 nm uniformly anchored on the reduced graphene oxide nanosheets, which are interconnected to form a porous graphene framework. The subsequent electrochemical measurements and kinetic analysis showed that the Ni0.31Co0.69S2/rGO composites possessed excellent electrocatalytic activity to glucose oxidation with a low detection limit of 0.078 μM and wide linear ranges of 0.001–5 mM and 5–16 mM. Moreover, the sensitivities for two linear ranges are 1753 μA mM−1 cm−2 and 954.7 μA mM−1 cm−2, respectively. In addition, the favorable selectivity, long-term stability and superior practical application were also obtained. All these results indicate that the Ni0.31Co0.69S2/rGO composites are a promising active material for non-enzymatic glucose sensors.

Transition-metal sulfides have attracted extensive interest as oxygen evolution reaction (OER) catalyst alternatives to noble metal based catalysts but generally exhibit limited electrocatalytic activity. We here report hierarchical porous Fe3O4/Co3S4 composite nanosheets for a highly efficient electrocatalytic OER in alkaline electrolytes. The preparation of the composite involves a hydrothermal synthesis and a subsequent sulfurization process. The prepared porous Fe3O4/Co3S4 composite shows strong synergetic coupling effects, facilitating active site exposure, and facile charge transfer. Remarkably, Fe3O4/Co3S4 nanosheets afforded an electrocatalytic OER with a current density of 10 mA cm−2 at a low potential of 1.50 V and a small Tafel slope of about 56 mV dec−1. This indicates that the composite of porous Fe3O4/Co3S4 nanosheets is promising as an efficient electrocatalyst for the OER that can be used in the fields of fuel cells, metal-air batteries and water splitting for hydrogen production.

A three dimensional (3D) nanostructured nickel oxide (NiO) electrode was fabricated by an electrodeposition method employing nickel foam (NF) as a scaffold and used for glucose detection. Taking advantage of the synergetic effect of NF and NiO, the 3D NiO/NF electrode shows excellent performance in glucose detection.

3D NiχCo1−χ oxides with different morphologies for high-capacity supercapacitors were controllably synthesized via an electrodeposition method combined with a simple post annealing process. The synthesis involves the co-electrodeposition of the bimetallic (Ni, Co) hydroxide precursor on a nickel foam scaffold and subsequent thermal transformation to NiχCo1−χ oxides. The crystalline structure, morphology and electrochemical performance of the 3D NiχCo1−χ oxides can be readily manipulated by simply varying the Co/Ni molar ratio in the electrodeposition electrolyte. With the increase of the Co/Ni molar ratio, the characteristic peak intensities and the signal sites were gradually changed from a NiO crystal dominant structure to NiCo2O4 and finally to a Co3O4 dominant structure. Moreover, the morphology also can be controlled by adjusting the Co/Ni molar ratio in the electrodeposition electrolyte. In addition, the Ni0.61Co0.39 oxide electrode shows a large specific capacitance of 1523.0 F g−1 at 2 A g−1 and 95.30% of that can be retained, even at a high current density of 30 A g−1. The superior rate capability should be attributed to the unique 3D network-like architecture, which can enlarge the liquid–solid interfacial area, facilitate the electron and ion transport, and further increase the utilization of the active material. To demonstrate its practical application, an asymmetric supercapacitor based on the Ni0.61Co0.39 oxide electrode as a positive electrode and activated carbon as a negative electrode was fabricated. Owing to the outstanding capacitive behavior of the Ni0.61Co0.39 oxide electrode, the asymmetric device delivers a prominent energy density of 36.46 W h kg−1 at a power density of 142 W kg−1, and which holds great promise for potential applications in energy storage.

Electrodeposited Ni(OH)2 on nickel foam with porous and 3D nanostructures has ultrahigh capacitance in the potential range −0.05–0.45 V, and a maximum specific capacitance as high as 3152 F g−1 can be achieved in 3% KOH solution at a charge/discharge current density of 4 A g−1.

Recently, transition metal-based nanomaterials have played a key role in the applications of supercapacitors. In this study, nickel phosphide (Ni-P) was simply combined with NiCo LDH via facile phosphorization of Ni foam and subsequent electrodeposition to form core–shell nanorod arrays on the Ni foam; the Ni-P@NiCo LDH was then directly used for a pseudocapacitive electrode. Owing to the splendid synergistic effect between Ni-P and NiCo LDH nanosheets as well as the hierarchical structure of 1D nanorods, 2D nanosheets, and 3D Ni foam, the hybrid electrode exhibited significantly enhanced electrochemical performances. The Ni-P@NiCo LDH electrode showed a high specific capacitance of 12.9 F cm−2 at 5 mA cm−2 (3470.5 F g−1 at a current density of 1.3 A g−1) that remained as high as 6.4 F cm−2 at a high current density of 100 mA cm−2 (1700 F g−1 at 27 A g−1) and excellent cycling stability (96% capacity retention after 10000 cycles at 40 mA cm−2). Furthermore, the asymmetric supercapacitors (ASCs) were assembled using Ni-P@NiCo LDH as a positive electrode and activated carbon (AC) as a negative electrode. The obtained ASCs delivered remarkable energy density and power density as well as good cycling performance. The enhanced electrochemical activities open a new avenue for the development of supercapacitors.

A novel photoelectrochemical (PEC) biosensing platform was constructed based on a ternary hybrid Ni/CdS/TiO2 nanotube array electrode, which was fabricated by the combination of electrochemical anodization and electrodeposition. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) confirmed that the CdS and Ni nanoparticles were homogeneously dispersed on the TiO2 nanotube arrays. Here, the Ni nanoparticles on the surface of CdS/TiO2 heterojunctions play a dual role in enhancing the performance of the PEC biosensor. First, Ni nanoparticles serve as a hole receptor, which can promote the fast charge separation and act as a protective layer that improves the stability of the Ni/CdS/TiO2 electrode. Second, Ni can remarkably improve the photoelectrochemical performance because it is a highly efficient electrocatalyst. As a result, the Ni/CdS/TiO2 nanotube array electrode offered much enhanced photocurrent compared to the CdS/TiO2 nanotube array electrode. Using glucose as a model, a highly sensitive photoelectrochemical biosensor based on the Ni/CdS/TiO2 nanotube array electrode was developed. Under optimized conditions, the biosensor displayed a wide linear range, a low detection limit as well as high selectivity and good stability. All these results indicate that this novel electrode is a promising candidate for use as a photoelectrochemical biosensor.

3D Ni3S2 nanosheet arrays grown on Ni foam were successfully synthesized through a facile one-step hydrothermal approach and then directly applied as the electrode for a high-performance supercapacitor and non-enzymatic glucose sensor. The structure and morphology of the prepared Ni3S2 were characterized by X-ray power diffraction (XRD), field emission scanning electronic microscopy (FESEM) and transmission electron microscopy (TEM). The subsequent electrochemical measurements showed that the Ni3S2 nanosheet array electrode possessed a superior specific capacitance of 1370.4 F g−1 at a current density of 2 A g−1. Remarkably, a specific capacitance of 952.0 F g−1 could be still achieved at a high current density of 20 A g−1, indicating its excellent rate capability. And 91.4% of the specific capacitance was retained after 1000 cycles at a current density of 6 A g−1. Besides, to demonstrate its practical application, an asymmetric supercapacitor based on the Ni3S2 nanosheet array electrode as the positive electrode and activated carbon as the negative electrode was assembled. It delivered high energy density and good long-term stability. Additionally, serving as a non-enzymatic sensor, the 3D Ni3S2 nanosheet array electrode exhibited remarkable electrocatalytic activity towards glucose oxidation with a high sensitivity of 6148.0 μA mM−1 cm−2. All these impressive performances suggest that the Ni3S2 nanosheet array is a promising electrode material for supercapacitors and non-enzymatic glucose sensors.

Mesoporous MnO2 nanowire array architecture exhibits enhanced capacitive and charge/discharge performance for electrochemical capacitors.