Efficient water splitting demands highly active, low cost, and robust electrocatalysts. In this study, we report the synthesis of penroseite (Ni,Co)Se2 nanocages anchored on 3D graphene aerogel using Prussian blue analogues as a precursor and further their applications in overall water splitting electrolysis. The synergy between the high activity of (Ni,Co)Se2 and the good conductivity of graphene leads to superior performance of the hybrid toward the water splitting in basic solutions. The (Ni,Co)Se2-GA only requires a low cell voltage of 1.60 V to reach the current density of 10 mA cm–2, making the (Ni,Co)Se2-GA hybrid a competitive alternative to noble metal based catalysts for water splitting.Keywords: graphene aerogel; HER; OER; penroseite (Ni,Co)Se2 nanocages; Prussian blue analogues;

•Chemical compositions and microstructure of magnetron sputtered CrNx coatings were studied.•Nano-composite coatings consisted of hexagonal Cr2N and fcc CrN phases are obtained.•Nano-composite coatings show both high hardness and good plastic deformation resistance.In this study, the CrNx coatings were deposited by reactive magnetron sputtering at varying sputtering power from 200 to 300 W. The chemical composition, phase structure, surface and cross-sectional morphologies, and mechanical properties of the coatings were respectively investigated by electron probe microanalysis, X-ray photoelectron spectroscopy, X-ray diffraction, Raman spectroscopy, scanning and transmission electron microscopy, and nano-indentation measurements. The results show that the coating deposited at a sputtering power of 200 W is a single-phase fcc CrN with columnar structure, while the coatings deposited at sputtering powers of 250 and 300 W are consisted of hexagonal Cr2N and fcc CrN with nano-composite structure. As compared with the single-phase Cr2N or CrN coatings, the composite coatings exhibit both higher hardness and superior resistance to plastic deformation and cracking, which is attributed to their unique nano-composite structure.

•PVD and thermal oxidation are combined to fabricate the Hf coating on Mg alloy.•Hf coating obtained by the hybrid methods exhibits nice protection for Mg alloy.•The relationship between microstructure and corrosion resistance was discussed.Low temperature thermal oxidation treatment is performed on the PVD (physical vapor deposition) hafnium-coated magnesium alloy. The results indicate that thin hafnium oxide film and new shallow grain boundaries were appeared on the coating surface. Surface oxidation and densification of the coating induced by the post treatment significantly decreased its susceptibility to corrosion. Moreover, the release of the residual stress produces a positive effect on suppressing the delaminating of the coating as magnesium is corroded. Consequently, the treated coating exhibits more positive corrosion potential, lower corrosion current density and higher polarization resistance than that of the untreated coating in Hanks’ solution. Salt spray test further reveals that the post-treated hafnium coating can provide a longer-term and more efficient protection for magnesium alloy.Download high-res image (262KB)Download full-size image

Supercapacitors have been becoming indispensable energy storage devices in micro-electromechanical systems and have been widely studied over the past few decades. Transition metal nitrides with excellent electrical conductivity and superior cycling stability are promising candidates as supercapacitor electrode materials. In this work, we report the fabrication of CrN thin films using reactive DC magnetron sputtering and further their applications for symmetric supercapacitors for the first time. The CrN thin film electrodes fabricated under the deposition pressure of 3.5 Pa show an areal specific capacitance of 12.8 mF cm−2 at 1.0 mA cm−2 and high cycling stability with 92.1% capacitance retention after 20 000 cycles in a 0.5 M H2SO4 electrolyte. Furthermore, our developed CrN//CrN symmetric supercapacitor can deliver a high energy density of 8.2 mW h cm−3 at the power density of 0.7 W cm−3 along with outstanding cycling stability. Thus, the CrN thin films have great potential for application in supercapacitors and other energy storage systems.

•The Hf/Si3N4 multilayer coatings were deposited on AZ91D Mg alloy.•The Hf/Si3N4 multilayer coatings exhibited superior anticorrosion performance.•The corrosion behaviors of the multilayer coatings were investigated.•The multilayer improved the corrosion resistance without sacrificing the conductivity.Hafnium monolayer and Hf/Si3N4 multilayer coatings were deposited on AZ91D magnesium alloys via magnetron sputtering. The microstructure, conductivity and corrosion behaviors of these coatings were investigated. It was found that the columnar growth of the Hf sublayer was suppressed in the Hf/Si3N4 multilayer coating. This multilayered structure resulted in the relief of residual stress and the decrease in porosity. These changes in microstructure inhibited the permeation of corrosion media into the substrate and decreased the diffusion rates of corrosion products. The Hf/Si3N4 multilayer coatings with 10 bilayers showed the best anticorrosion performance revealed by the lowest corrosion current density of 2.798 μA/cm2 in electrochemical system and the smallest corrosion area of 0.22% after 48 h salt spray test, respectively. Additionally, the introduction of Si3N4 sublayer has little impact on the conductivity of the multilayer coating due to the shadowing effect during the deposition.

•High-temperature wear tests of the Ti0.53Al0.47N coatings were carried out.•The maximum test temperature was elevated to 850 °C during the wear test.•XPS analysis and AES depth profiling of the oxide scales formed at RT–850 °C.•Relationship between wear mechanism and working temperature was discussed.In this study, oxidation and tribology behavior of Ti0.53Al0.47N coating deposited by cathodic arc evaporation were investigated. The effects of varying temperature from RT to 850 °C on microstructure, phase composition, oxidation behavior, and wear resistance of the coating were evaluated. The phase structure of the Ti0.53Al0.47N coating changes slightly with the elevated temperature, whereas the oxidation behavior of the coating reveals a remarkable variation due to the formation of different type oxide scales. The final oxide scale consists of an outer Al2O3 dominated layer and an inner TiO2 dominated layer, exhibiting a bilayer structure. A serious wear of the Ti0.53Al0.47N coating occurs during the room temperature test. With increasing the test temperature up to 700 °C, the coating show promoted wear resistance owing to the Al2O3 oxide scale provides an excellent protection against the wear. However, further increasing the temperature up to 850 °C produces a fast growth of the TiO2. This deteriorates the protection of the Al2O3 scale, resulting in an accelerated oxidation of the coating. Consequently, the Ti0.53Al0.47N coating illustrates a degraded wear resistance at 850 °C.

•Chemical and phase compositions and microstructure of NbNx coatings were investigated.•Maximum hardness is obtained for nano-composite coating with mixed Nb2N and NbN phases.•Activation energies are 219.3 and 192.3 kJ/mol for oxidation of Nb2N and NbN coatings.•Non-protective Nb2O5 scales with cracks and pores lower oxidation resistance of NbN coating.Mechanical properties and oxidation resistance are of importance for the NbNx coatings as used in cutting and forming tools. In this study, the NbNx coatings were deposited by magnetron sputtering at nitrogen partial pressure ranging from 0 to 40%. The chemical and phase compositions, morphologies, mechanical properties and oxidation behaviors of the NbNx coatings were investigated by electron probe microanalysis, X-ray photoelectron spectroscopy, grazing incidence X-ray diffraction, scanning and transmission electron microscopy, and nanoindentation measurements. The results reveal the composition evolution of the NbNx coatings as α-Nb (0%), β-Nb2N (5%), a mixture of β-Nb2N and δ-NbN (10%), and δ-NbN (20–40%). The single phase coatings exhibit columnar structure while the mixed phases coating shows nano-composite structure. Compared with the single phase δ-NbN coatings (21.6 ± 0.8–28.0 ± 1.2 GPa), higher hardness of the single phase β-Nb2N coating (30.9 ± 1.0 GPa) is due to the higher covalent character and much finer grains. The maximum hardness reaches 33.3 ± 1.5 GPa for the nano-composite coating with mixed phases of β-Nb2N and δ-NbN. The oxidation results demonstrate that the activation energies are 219.3 and 192.3 kJ/mol for the Nb2N and NbN coatings respectively. Non-protective Nb2O5 scales with cracks and pores result in poorer oxidation resistance of the NbN coating in comparison to the Nb2N coating.

In this paper, dandelion-like ZnS was synthesized via a facile hydrothermal method, and then as the support to further synthesize dandelion-like ZnS/carbon quantum dot hybrid materials. Multiple techniques were applied to investigate the structures, morphologies, electronic and optical properties of the samples. It can be observed that the carbon quantum dots were distributed uniformly on the surface of the ZnS. The photocatalytic activities of the as-prepared materials were investigated by the photodegradation of methylene blue, Rhodamine B and the colorless antibiotic ciprofloxacin hydrochloride, respectively. The as-synthesized hybrid materials exhibit higher photocatalytic activity than that of the pure ZnS under simulated sunlight (λ > 380 nm), indicating a broad-spectrum of photocatalytic degradation activity. The most beneficial amount of carbon quantum dots to improve the photocatalytic activity of the ZnS is 2.0 wt%.

This work investigates microstructure, hardness and deformation behaviors of Zr–Si–N nanocomposite coatings with 0–20.9 at.% Si. Relationship between the hardness evolution and the deformation behaviors of the nanocomposite coatings was discussed as well. Dislocation glides together with microcrack initiation and propagation contribute to the plastic deformation of the nanocomposite coatings. The microcrack propagation along the columnar, yet weak bonded grain boundaries is found to be the primary factor inhibiting the hardness improvement of the Si-free ZrN coating. The Zr0.963Si0.037N0.916 coating exhibits the highest recorded hardness of 33.2 ± 1.0 GPa. The amorphous matrix exhibits a high energy of microcrack formation and propagation when the nanocomposite coating is exposed to indenter. The microcracks produced by nanoindentation in the Zr0.963Si0.037N0.916 coating preferentially propagate into the ZrN nanocrystals rather than along the grain boundaries. Both effects of grain size refinement and grain boundary strengthening result in the hardness improvement.

•3D porous hybird aerogel assembly of Bi2WO6 nanosheets and graphene was firstly prepared via a facile solvothermal route.•The Rhodamine B (RhB) removal ratio over the 3D hybird aerogel photocatalyst reaches up to 99.6% within 45 min•Graphene could promote the separation of photocarriers by removing photo-generated electrons from Bi2WO6.•The O2−• is the main active species for the degradation of the RhB.A three-dimensional porous hybrid aerogel assembly of Bi2WO6 nanosheets and graphene has been prepared by a facile solvothermal route. The products are characterized by X-ray diffraction, Scanning electron microscope, Transmission electron microscopy, and so on. The results show the highly interconnected and porous network microstructure stacked by graphene and Bi2WO6 nanosheets in the hybrid aerogel. The specific surface area of hybrid aerogel (39.4 m2 g−1) is 1.6 times higher than that of Bi2WO6 nanosheets. The Rhodamine B removal ratio over the composite aerogel reaches up to 99.6% within 45 min, which is higher than that of pure Bi2WO6 nansosheets (80%). The excellent photocatalytic performance is mainly owing to the porous structure of aerogel and high electrical conductivity of graphene. The study on the photocatalytic mechanism demonstrates that O2−• is the main reactive species for Rhodamine B degradation.

•Microstructure evolution of nano-indented zone of ZrN was investigated.•Dislocation glide, crack initiation and propagation result in the deformation.•Intergranular fracture by crack propagation along the GBs was found.Microstructure evolution of nano-indented zone of nanocrystalline ZrN coating has been investigated by transmission electron microscopy. Dislocation glides together with microcrack initiation and propagation contribute to the plastic deformation of the ZrN coating. The dislocation density of the deformed zone reaches ~3×1012 cm−2. The microcracks preferentially initiate just underneath the contact surface and then propagate along the columnar yet weak bonded grain boundaries. The microcrack propagation is found to be the probable factor deteriorating the coating hardness. Strategy to improve the coating hardness via strengthening the grain boundaries has been discussed.

•Spinel Li2Cu0.5Mn0.5Ti3O8 is prepared by a simple solid state reaction.•Li2Cu0.5Mn0.5Ti3O8 shows better electrochemical property than Li2CuTi3O8 and Li2MnTi3O8.•Li2Cu0.5Mn0.5Ti3O8 reveals a reversible capacity of 143 mAh g−1 after 50 cycles.In this article, Cu2+ and Mn2+ are chosen as divalent metal cations to dope and synthesize Li2MTi3O8 (M = Cu, Mn, Cu0.5Mn0.5) by a simple solid state reaction route. The structures of Li2MTi3O8 (M = Cu, Mn, Cu0.5Mn0.5) are proved by Rietveld refinement method for the first time. Due to different divalent metal cations M2+ in the structure, Li2MTi3O8 exhibits different electrochemical performances. Li2CuTi3O8 shows the highest initial charge capacity of 242 mAh g−1 and Li2MnTi3O8 displays the lowest initial charge capacity of 139.5 mAh g−1 among all the three samples. Although Li2Cu0.5Mn0.5Ti3O8 reveals a lower initial charge capacity of 174.5 mAh g−1, it exhibits better cycle performance than Li2CuTi3O8 and Li2MnTi3O8. Li2Cu0.5Mn0.5Ti3O8 keeps the reversible capacity of 143 mAh g−1 after 50 cycles at 100 mA g−1 with capacity retention of 82.2%. Besides, the results of electrochemical impedance spectra indicate that lithium ion can move easily in the tunnels of three-dimensional network formed by the (Li0.7Cu0.15Mn0.25)tet, which is in agreement with the result that Li2Cu0.5Mn0.5Ti3O8 performs better electrochemical properties than Li2CuTi3O8 and Li2MnTi3O8. It provides a possibility and theoretical support to synthesize Ti-based materials Li2MTi3O8 with good electrochemical performances.

•Hierarchical layer-by-layer LaCO3OH was prepared by hydrothermal method.•Layer-tunable LaCO3OH can be obtained by adjusting the addition volume of CS2.•The 3D multilayer LaCO3OH emits stronger fluorescence than the 2D microplates.Hexagonal LaCO3OH with layer-tunable microstructures have been synthesized by a facile hydrothermal method. Typically, two-dimensional (2D) LaCO3OH microplates and three-dimensional (3D) layer-by-layer (LBL) LaCO3OH were produced by simply adjusting the experimental parameters. In the synthetic procedure, the volume of carbon disulfide (CS2) added to the reaction mixture was found to be crucial in the formation of the layer-tunable microstructures. A possible formation mechanism of the LBL LaCO3OH has been also proposed from a temporal evaluation of the products. Furthermore, photoluminescence (PL) study demonstrated that the LBL LaCO3OH emitted stronger fluorescence than the single layer microplates.

•Hierarchical coral-like Co-doped ZnS was prepared by hydrothermal method.•Co-doping enhances the absorption of visible light of the ZnS.•Co-doping inhibits the recombination of photoinduced charge carriers.•A 5.49 at.% Co content guaranteed higher photocatalytic activity.A series of coral-like Co-doped ZnS were synthesized by hydrothermal method and used for efficient photodegradation of methylene blue. The chemical composition and microstructure of the Co-doped ZnS were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, UV–vis diffuse reflectance spectra, scanning electron microscope, and transmission electron microscopy. The results showed that the Co atoms were incorporated into the Zn-S lattice, forming solid solution-type phase. As the Co dopant concentration increases from 0 to 22.49 at.%, the calculated band gap energy of the doped ZnS decreases from 3.32 to 2.65 eV, which enables stronger absorption of visible light. Furthermore, the Co dopant could act as electron trapping center, which inhibits the recombination of the photoinduced electrons and holes. As such, the Co-doped ZnS micro-corals showed higher photodegradation efficiency for methylene blue compared with pristine ZnS. The optimized photocatalytic activity was achieved on 5.49 at.% Co-doped ZnS.

•Nb addition improves the hardness of the Cr–Nb–N coatings.•Significantly improvements in oxidation resistance are achieved by Nb addition.•TEM micro-structural study of the monocrystalline α-Cr2O3 granulesIn this study, Cr–Nb–N coatings with a 0–1.7 at.% Nb addition were fabricated by magnetron co-sputtering deposition in an Ar–N2 mixture atmosphere. The influence of Nb addition to the microstructure, indentation hardness and oxidation resistance of the CrN coating has been investigated. The results reveal that the Nb ions substitute the Cr ions in the Cr–N lattice, forming the solid solution-type coatings. All the cross-sectional morphologies of the Cr–Nb–N coatings illustrate a dense and columnar microstructure, showing independent of Nb content. Nevertheless, incorporating the Nb into the CrN provides a favorable condition for the grain size refinement of the coating. In addition, improving the Nb content promotes the preferred growth of the (1 1 1) grains. Nanoindentation tests reveal an enhanced hardness of the coatings from 15.2 ± 0.6 to 19.1 ± 0.7 GPa with increasing the Nb content from 0 to 1.7 at.% due to both the solid solution strengthening and the grain size refinement. The oxidation results demonstrate that the most beneficial addition of the Nb to improve the oxidation resistance of the CrN coating is 0.5 at.%. An excessive addition of Nb deteriorates the oxidation resistance. The outward diffusion of the Cr ions will be effectively blocked by the preferential transport of the larger Nb ions, resulting in the improved oxidation resistance.

•Al, Ti, Zr and Hf coatings were fabricated on Mg alloy by magnetron sputtering.•The Hf coating exhibits superior anti-corrosion performance.•The corrosion mechanisms of the metallic coatings were comparatively discussed.This paper focuses on the deposition of anti-corrosion, conductive coatings for Mg alloys used in electronics and aerospace industries. Metallic Al, Ti, Zr and Hf coatings were fabricated on an AZ91D Mg alloy surface via magnetron sputtering. Electrochemical system and salt spray tests were performed to investigate the corrosion resistance and the mechanism of corrosion failure of coated samples. The Hf-coated Mg alloy exhibited an extremely low corrosion current density of 0.825 μA/cm2 and a high protective efficiency of 99.49% during the electrochemical test. More importantly, the Hf coating provided superior protection for the Mg alloy against corrosion during the 24 h salt spray test. However, the Al-, Ti- and Zr-coated alloys exhibit poor performances in the above measurements. The low difference in potentials, the excellent corrosion resistance and the good adhesion to the substrate are considered probable causes for the anti-corrosion performance of the Hf coating.

Porous materials are of particular interest due to their high surface area and rich edge sites, which are favorable for applications such as catalysis. Although there are well-established strategies for synthesizing porous metal oxides (e.g., by annealing the corresponding metal hydroxides), facile and scalable routes to porous metal hydroxides and metal chalcogenides are lacking. Here, we report a simple and general strategy to synthesize porous nanosheets of metal hydroxides by selectively etching layered double hydroxide (LDH) nanoplate precursors that contain amphoteric metal and to further convert them into porous metal chalcogenides by a solution method. Using NiGa LDH as an example, we show that the thin nanoplates with high surface accessibility facilitate the topotactic conversion of NiGa LDH to β-Ni(OH)2 and further to NiSe2 with porous texture while preserving the sheet-like morphology. The converted β-Ni(OH)2 and NiSe2 are highly active for electrocatalytic oxygen evolution reaction and hydrogen evolution reaction (HER), respectively, which demonstrates the applications of such high surface area porous nanostructures with rich edge sites. Particularly, the porous NiSe2 nanosheets exhibited excellent catalytic activity toward HER with low onset overpotential, small Tafel slope, and good stability under both acidic and alkaline conditions. Overall electrochemical water splitting experiments using these porous β-Ni(OH)2 and NiSe2 nanosheets were further demonstrated. Our work presents a new strategy to prepare porous nanomaterials and to further enhance their catalytic and other applications.

•Li2CuTi3O8 with the space group of Fd-3m is synthesized for the first time.•Li2CuTi3O8 exhibits stable host structure for lithium storage.•Li2CuTi3O8 can deliver a reversible capacity of 203 mAh g−1 after 50 cycles.•Lithium storage mechanism in Li2CuTi3O8 is proposed for the first time.Complex spinel Li2CuTi3O8 with a space group of Fd-3m is prepared for the first time by a simple solid state reaction route. This compound has different space group from the previous reported Li2MTi3O8 (M = Zn, Co, Mg, Ni and Mn) with a space group of P4332. It shows reversibility for lithium storage in the cubic structure. A reversible capacity of 203 mAh g−1 can be delivered at a current density of 100 mA g−1 after 50 cycles with the capacity retention of 70.7%. The electrochemical reaction mechanism between Li2CuTi3O8 and lithium is investigated by various in-situ and ex-situ observations. Rietveld refinement results show that Li2CuTi3O8 has multiple interstitials to accommodate lithium ions during the lithiation process, in which the irregular octahedral 32e sites would be occupied by lithium ions at high working potentials and the regular octahedral 16c sites would be occupied by lithium ions at low working potentials. Besides, a reversible migration of copper ions can found during discharge process. Based on the reverse delithiation process, it is known that the whole charge–discharge process is quasi-reversible for Li2CuTi3O8. Therefore, Li2CuTi3O8 shows high structural stability as a promising lithium storage material for lithium-ion batteries.

In this work, spinel Li2MnTi3O8 is successfully prepared by using a simple sol-gel route and evaluated as an anode material for lithium-ion batteries. Charge-discharge tests exhibits than spinel Li2MnTi3O8 can deliver an initial discharge capacity of 273.5 mAh g−1 and the reversible capacity is kept at 206.1 mAh g−1 after 50 cycles, corresponding to 94.5% of the initial charge capacity. The electrochemical reaction mechanism between Li2MnTi3O8 and lithium is investigated based on the results of various in-situ and ex-situ observations. The result indicates that the (Li0.505Mn0.495)tet(Li0.495Mn0.005)octTi1.5octO4 has multiple interstitials to accommodate lithium ions during the lithiation process, in which the octahedral sites (4a) would be occupied by lithium ions at high working potential and the tetrahedral sites (8c) would be occupied by lithium ions at low working potential. As a result, two two-phase transitions between three end-number phases Li2MnTi3O8, Li3MnTi3O8 and Li5MnTi3O8 can be observed during the reversible electrochemical reaction between Li2MnTi3O8 and lithium.

Microstructure evolution during oxidation of ZrN coating at 650 °C was investigated by in situ and ex situ methods. The results reveal the simultaneous occurrence of epitaxially growing tetragonal ZrO2 near the ZrO2–ZrN interface and transformation from preformed tetragonal to monoclinic phase close to the oxide surface. The significant volume expansion associated with tetragonal → monoclinic transformation plays a major role in producing interconnected microcracks and pores across the oxide scale, which provide fast diffusion paths of oxygen and hence lower the oxidation resistance of ZrN coating.

A series of Li2−xNaxZnTi3O8 (x = 0, 0.05, 0.10, 0.15, 0.20) are prepared for the first time by a simple solid state method. Upon Na-doping, Rietveld refinement reveals that Na+ takes the 8c tetrahedral sites shared with Li+ and Zn2+ in the structure. Due to the larger ionic radius of Na+ than that of Li+, an increased disorder degree of ion locations in the structure is induced by Na doping. Furthermore, the lithium ion diffusion tunnel is also expanded after Na doping. Thus, higher lithium ion diffusion coefficient can be observed for all the Na-doped Li2ZnTi3O8 samples. However, phase analysis shows that high Na-doping content can result in the formation of impurity in the as-obtained titanates. Besides, the existence of too many Na ions in the spinel also decreases the structural stability. Therefore, Na-doping with low dose is beneficial to improve the electrochemical performance of Li2ZnTi3O8. Electrochemical evaluations show that Li1.95Na0.05ZnTi3O8 has the best lithium storage property among all the Li2−xNaxZnTi3O8. It can be found that Li1.95Na0.05ZnTi3O8 can deliver a reversible capacity of 267.3 mA h g−1 after 50 cycles. This finding can provide an experimental support to synthesize high performance Ti-based materials by Na doping.

•Moderate Hf addition improves the hardness of the (Zr, Hf)Nx coatings.•Significantly improvements in oxidation resistance are achieved by Hf addition.•Raman scattering and TEM microstructural studies of the oxide scalesThis study investigates the influence of Hf addition to the microstructure, mechanical properties and oxidation resistance of ZrN coating. (Zr, Hf)Nx coatings with 0–4.2 at.% Hf were fabricated by reactive co-sputtering in an Ar–N2 atmosphere. The solid solution-type (Zr, Hf)Nx coatings exhibit a dense and columnar structure with strong (2 0 0) preferred orientation, independent of Hf content. Abnormal grain growth was observed in the coatings with improved Hf content. The highest recorded hardness is 28.6 ± 0.6 GPa with 0.5 at.% Hf addition, whereas further increasing the Hf content up to 4.2 at.% decreases the hardness. The oxidation results demonstrate that the most beneficial content of Hf to improve the oxidation resistance of the ZrN coating is 1.2 at.%. Reduction in inward diffusion paths for oxygen ions, the increase of stoichiometry and the high thermal stability of HfN have been identified as the primary reasons for the improvements of the oxidation resistance.

Hematite (α-Fe2O3) concave nanocubes bound by high-index {134} and {128} facets were synthesized and their catalytic activity for CO oxidation were also investigated.

α-Fe2O3 2D hollow microplatelets were synthesized by a facile one-pot template-free solvothermal method. The effect of synthetic parameters on the morphology and structure of the product was systematically studied. And the possible formation mechanism was proposed. Interestingly, by simply varying the concentration of NH4F, α-Fe2O3 hollow microstructures with similar platelet-like shapes but different porosities can be readily obtained. Their comparative photocatalytic activities were also investigated.

Hematite nanostructures with similar spindle-like shapes but different hollowness and porosities have been prepared by a facile hydrothermal method. The comparative photocatalytic activities of these samples were investigated and the results might be helpful to further understand the beneficial effects of hollow and porous structures.

•Li2Zn0.5Cu0.5Ti3O8 was prepared by a simple solid state reaction.•Li2Zn0.5Cu0.5Ti3O8 shows better electrochemical property than Li2CuTi3O8 and Li2ZnTi3O8.•Li2Zn0.5Cu0.5Ti3O8 can deliver a reversible capacity of 162 mA h g−1 after 50 cycles.In this work, complex spinel titanates Li2MTi3O8 (M = Zn, Cu, Zn0.5Cu0.5) have been synthesized by a simple solid state reaction route. Their crystal structures are described and verified by Rietveld refinement. Electrochemical results exhibit that Li2CuTi3O8 has a highest lithium storage capacity of 242 mA h g−1 and Li2ZnTi3O8 displays the lowest initial charge capacity of 190 mA h g−1 among all the three samples. However, both Li2CuTi3O8 and Li2ZnTi3O8 show poor capacity retention and low reversible capacity after 50 cycles. Li2Zn0.5Cu0.5Ti3O8 shows higher structural and cycling stability than that of Li2ZnTi3O8 and Li2CuTi3O8. As a result, Li2Zn0.5Cu0.5Ti3O8 can deliver a reversible capacity of 162 mA h g−1 after 50 cycles with capacity retention of 74%.Graphical abstract

•Promoted hardness of CrAlN coatings with Y addition due to solid solution strengthening and Hall–Petch effect.•0.3 and 0.7 at.% Y additions improve the oxidation resistance of the CrAlN coatings.•More than 1.3 at.% Y addition deteriorates the oxidation resistance of the CrAlN coatings.This study aims to investigate the influence of Y content on microstructure, hardness and oxidation resistance of the quaternary CrAlYN hard coatings. The CrAlYN coatings were deposited by magnetron co-sputtering using Cr50Al50 composite and pure Y targets. The Y content increases from 0 to 2.3 at.% with Y target power increasing from 0 to 150 W while Cr50Al50 target power keeping constant at 250 W. Electron probe microanalysis (EPMA) and X-ray diffraction (XRD) results indicate that Y atoms substitute Cr and/or Al atoms in CrAlN lattice forming the solid solution CrAlYN coatings. The surface and cross-sectional morphologies of the CrAlYN coatings exhibit tapered grains and columnar structure respectively. Moreover, the tapered grain sizes and the column widths decrease with increasing Y content. Nanoindentation result reveals a promoted hardness of the CrAlYN coatings from 16.9 ± 0.8 GPa to 24.1 ± 1.0 GPa with enhanced Y content from 0 to 2.3 at.% due to both of the solid solution strengthening and Hall–Petch effect. The oxidation result demonstrates that the Y content beneficial for the oxidation resistance of the CrAlYN coatings is between 0.3 and 0.7 at.%. Excess Y addition (≥ 1.3 at.%) significantly deteriorates the oxidation resistance of the CrAlYN coatings as a result of the formation of porous and non-protective oxide scales.

Hollow structures are attracting increasing attention due to their unique properties and potential applications in many fields. Despite the great successes achieved in the synthesis of hollow spheres, the preparation of nonspherical hollow structures still remains a great challenge. In this paper, we developed a facile method to prepare hematite hollow structures with cocoon-like shape. The as-prepared hematite nanococoons were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM). Such cocoon-like structures are with a uniform diameter of 18 nm, length of 90 nm, and shell thickness of 5 nm. Furthermore, the as-prepared sample exhibited high visible-light photocatalytic activity for the degradation of methyl orange due to their special hollow structure.Highlights► Nonspherical hollow hematite nanostructures with cocoon-like shape have been synthesized. ► Hematite hollow cocoons were obtained by annealing treatment of silica-coated β-FeOOH nanorods. ► Photocatalytic activity of such novel hollow structures was investigated.

•3D flower-like hematite microstructures were synthesized by a hydrothermal method.•The formation mechanism of flower-like microstructures was proposed.•Effective removal of As(V) and Cr(VI) from aqueous solution.Hierarchically 3D flower-like α-Fe2O3 microstructures have been synthesized through a urea-assisted hydrothermal synthetic route. The product was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The as-prepared product was consisted of hierarchically flow-like microstructures assembled from nanopetal subunits. The effects of the urea and NaOH on the morphology of the products were systematically studied, and a possible formation mechanism of the α-Fe2O3 microflowers was proposed based on the experimental results. These flower-like α-Fe2O3 microstructures were used as adsorbent for water treatment, and the results revealed excellent performance for heavy metal ion removal. With maximum capacities of 41.46 and 33.82 mg g−1 for As(V) and Cr(VI), respectively, such flower-like α-Fe2O3 microstructures are expected to be an attractive adsorbent for the removal of heavy metal ions from water.

ZrYN coatings with various yttrium contents (0 to 15 at.% in the targets) are deposited from zirconium yttrium composite targets using DC magnetron sputtering. The effect of varying amounts of yttrium addition on the microstructure and mechanical properties of ZrN coatings has been studied. The results reveal that yttrium atoms substitute zirconium atoms in Zr–N lattice forming the solid solution ZrYN coatings. The preferred orientation changes from (200) to (111) with yttrium addition, while the grain sizes are approximately the same. The indentation hardness of the ZrYN coatings first increases from 19.7 GPa to 24.1 GPa with increasing yttrium content up to 5 at.% and is followed by a decrease to 20.9 GPa with a further increase in yttrium content. Scratch test shows that yttrium addition has a beneficial effect on the adhesion of the ZrYN coatings with the critical load increasing from 2.8 N for the ZrN coating to 7.6 N for the ZrYN coating (yttrium content 10 at.%).Highlights►Study on the microstructure and mechanical properties of ZrYN coatings. ►Correlation of XRD, Raman spectroscopy and SAED analysis. ►TEM and XRD analysis for grain size. ►Explanations for evolution of preferred orientation and grain size. ►Moderate yttrium addition improves the hardness and adhesion of ZrYN coatings.

In this study, Ti0.34Al0.66N coatings were fabricated by arc ion plating (AIP) process on ceramic carbide substrates. The tribological tests were carried out by using a ball-on-disc tribometer with different temperatures from 25 °C to 900 °C in air. After high-temperature testing, the microstructure, chemical composition, oxidation behavior and mechanical properties were investigated using X-ray diffraction, Auger electron spectroscopy, X-ray photo-electron spectroscopy, scanning electron microscopy and nanoindentation tests. Phase separation and crystallization of oxide layer occurred at 900 °C. The decrease of surface hardness and significant improvements on wear resistance were obtained at high temperatures, which were connected to the oxidation behavior of Ti0.34Al0.66N coatings. The results showed that the formation of oxide layer determined the contacting state between the slider and coatings at elevated temperatures, and was responsible for the changes in wear mechanisms.Highlights► High-temperature tribological tests of Ti0.34Al0.66N coatings up to 900. ► XPS and AES analysis on the oxidation behavior. ► The wear mechanisms at different temperatures were respectively discussed. ► The relationship between tribological properties and oxidation behavior.

A comparative study of the oxidation behavior of Cr2N and CrN coatings was investigated in air at temperatures ranging from 700 °C to 1000 °C including phase structure, surface and cross-sectional morphologies, oxidation kinetics and mechanism. During oxidation, the dense Cr2O3 scales form both on the Cr2N and CrN coatings. The Cr2N phase transforms to CrN phase, which is accompanied with 20% volume expansion in transverse. This volume expansion induces the porous and non-columnar cross-sectional morphology of the Cr2N coating. The worse oxidation resistance of the Cr2N coating compared with the CrN coating is attributed to its higher chromium content and phase transformation induced porous structure. The oxidation activation energy values are 139 and 190 kJ/mol for the Cr2N and CrN coatings respectively, which is comparable to the literature results. Marker experiments prove that the growth of Cr2O3 scales is controlled by both the outward diffusion of chromium and inward diffusion of oxygen and the outward diffusion of chromium is dominated.Highlights► Morphological changes of Cr2N and CrN coatings after oxidation ► Phase transformation from Cr2N to CrN during oxidation ► Relation among phase structure, morphologies and oxidation resistance ► Study of oxidation mechanisms of nitride hard coatings by marker experiments

Two kinds of pH-dependent magnetic nanoadsorbent based on silica-coated MnFe2O4 nanoparticles (SMNPs) and amino-modified silica-coated MnFe2O4 nanoparticles (AS-MNPs) have been synthesized using sol–gel method. X-ray diffraction, Fourier transform infrared spectroscopy and transmission electron microscopy have been employed to characterize the structure and morphology of the nanoadsorbents. The magnetic properties and zeta potential were also investigated. These nanoadsorbents were used to adsorb bovine serum albumin (BSA). The adsorption capacity of BSA largely depended on the pH and ionic strength of solution. In the best result, BSA was adsorbed on AS-MNPs at a high value of 164 mg g−1, which is much higher than that of SMNPs (100 mg g−1). This may due to the increased surface amino that can be conjugated to BSA by a chemical bond and the electrostatic attraction between BSA and magnetic nanoparticles.

Single-crystalline α-Fe2O3 with a micro-snowflake-like morphology has been synthesized though a hydrothermal reaction in a K3[Fe(CN)6] solution without the assistance of any template or surfactant. The morphology and structure of the synthesized hematite were characterized in detail by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. A possible growth process of α-Fe2O3 crystals has been proposed, and NaOH plays a crucial role in the formation of the snowflake-like structure. Additionally, magnetic investigations show that the α-Fe2O3 crystals exhibit a weakly ferromagnetic property at room temperature with a coercive force of 134 Oe and remnant magnetization of 0.67 emu g− 1.

This work describes a novel fabrication technique to prepare yttria-stabilized zirconia (YSZ) thin films by electrostatic spray deposition (ESD) from suspension. A detailed discussion on the formulation of colloidally stable suspension to prepare dense and uniform YSZ thin films is presented in this study. X-ray diffraction (XRD) and scanning electron microscopy (SEM) are used to analyze the structure and morphology of the YSZ thin films. The results show that a mixture of acetylacetone and ethanol in a ratio of 1:1 by volume is an effective suspension medium for YSZ fine particles to produce colloidally stable suspension, and the YSZ thin films with uniform in thickness about 2 μm and densely packed can be obtained by ESD from the suspension.

Cr1-xYxN coatings were fabricated by reactive co-sputtering deposition and the Y content was changed by varying the Y target power. The influence of varying amounts of Y addition on the mechanical properties and oxidation resistance of CrN coatings has been studied. The results reveal that Y ions substitute Cr ions in Cr-N lattice forming the solid solution Cr1-xYxN coatings. Y doping has a beneficial effect on the improvements of hardness and adhesion of the coatings. After the oxidation in air at 850 °C for 2 h, The CrN coating with 1.2 at. % Y addition exhibits superior oxidation resistance than Y-free CrN coating, while over doping of Y produces detrimental effects on oxidation resistance of the coatings.

The aim of the present research was to investigate the influence of different substrate roughness on structure and mechanical properties of Titanium Aluminium Nitride (TiAlN) coatings. Tungsten carbide rectangular block was used as substrate. Different surface roughness was achieved by using grinding discs with different grain sizes and diamond polishing powder, and TiAlN coatings were deposited on these substrates under the same preparation technique and parameters. Morphologies of substrates and coatings, crystal structure, thickness and mechanical properties of coatings were investigated using optical microscope, AFM, XRD, CSM scratch tester and tribometer. It was shown that surface morphology of cathodic arc TiAlN coating was mainly affected by the morphology of the substrate surface and the coating growth process. The influence of substrate roughness on crystal structure and thickness of the coatings could be ignored. With the decreasing of the substrate roughness, the adhesion force between coating and substrate increased. Three stresses model was applied to interpret this result. The wear resistance of the coating was also improved with decreasing the substrate roughness.

Supercapacitors have been becoming indispensable energy storage devices in micro-electromechanical systems and have been widely studied over the past few decades. Transition metal nitrides with excellent electrical conductivity and superior cycling stability are promising candidates as supercapacitor electrode materials. In this work, we report the fabrication of CrN thin films using reactive DC magnetron sputtering and further their applications for symmetric supercapacitors for the first time. The CrN thin film electrodes fabricated under the deposition pressure of 3.5 Pa show an areal specific capacitance of 12.8 mF cm−2 at 1.0 mA cm−2 and high cycling stability with 92.1% capacitance retention after 20000 cycles in a 0.5 M H2SO4 electrolyte. Furthermore, our developed CrN//CrN symmetric supercapacitor can deliver a high energy density of 8.2 mW h cm−3 at the power density of 0.7 W cm−3 along with outstanding cycling stability. Thus, the CrN thin films have great potential for application in supercapacitors and other energy storage systems.

It is of prime importance to develop dual-functional electrocatalysts with good activity for overall water splitting, which remains a great challenge. Herein, we report the synthesis of a Co-doped nickel selenide (a mixture of NiSe2 and Ni3Se4)/C hybrid nanostructure supported on Ni foam using a metal–organic framework as the precursor. The resulting catalyst exhibits excellent catalytic activity toward the oxygen evolution reaction (OER), which only requires an overpotential of 275 mV to drive a current density of 30 mA cm−2. This overpotential is much lower than those reported for precious metal free OER catalysts. The hybrid is also capable of catalyzing the hydrogen evolution reaction (HER) efficiently. A current density of −10 mA cm−2 can be achieved at 90 mV. In addition, such a hybrid nanostructure can achieve 10 and 30 mA cm−2 at potentials of 1.6 and 1.71 V, respectively, along with good durability when functioning as both the cathode and the anode for overall water splitting in basic media.

α-Fe2O3 2D hollow microplatelets were synthesized by a facile one-pot template-free solvothermal method. The effect of synthetic parameters on the morphology and structure of the product was systematically studied. And the possible formation mechanism was proposed. Interestingly, by simply varying the concentration of NH4F, α-Fe2O3 hollow microstructures with similar platelet-like shapes but different porosities can be readily obtained. Their comparative photocatalytic activities were also investigated.