Synthesis And Properties Of Three-dimensional Integrated Nickel-based Electrodes For Hydrogen Evolution Reaction

Among the numerous non-precious metal based electrocatalysts,nickel-based electrocatalysts possess near optimum hydrogen adsorption free energy changes(ΔG_H*)and exchange current density（j₀）.However,their industrialized application is encumbered by their low intrinsic activity,insufficient exposure of active sites,and relative low stability.In this paper,constructing the 3D structure integrate electrode has been provided to improve their activity and stability.Based on this,two different experiment has been performed:（1）A“superaerophobic”NiCoP/Ni electrocatalyst has been prepared by employing the bimetal-organic frameworks as self-sacrificing templates.The NiCoP/Ni possess 3D complex structures.The hollow microprism as the frame structure can form an open,and connected channel to promote the transfer of electrolyte and the produced H₂ bubbles,and the nanoneedles growth on the surface of hollow microprism can provide large numbers of actives sites for HER.（2）The 3D structure Co/WO₂/NiW electrocatalysts by employing the Co₃O₄ nanowires as templates.The interaction between NiW alloy and WO₂ can optimize the hydrogen absorption free energes changes(ΔG_H*)and therefore,enhance the HER activity in alkaline solution.1.Construction of MOF-derived NiCoP/Ni nanocages/nanowires catalysis for HER.In this part,the“superaerophobic”NiCoP/Ni nanocages/nanowire were syntheszied by employing the bimetal-organic frameworks as self-sacrificing templates.Firstly,the solid Ni Co bimetal-organic framework with the morphology of microprism is obtained by terephalic acid（BDC）as the ligand,Ni（NO₃）₂·6H₂O and Co（NO₃）₂·6H₂O as the nickel and cobalt sources.In the second step,the solid Ni Co-MOF will transform into a hollow microprism structure cladded by order-oriented nanoneedles through a second hydrothermal reaction in urea solution.At last,the NiCoP/Ni can be obtained via phosphation at specified temperatures in a quartz furnace.SEM images indicated that many small nanoneedles with average length and diameter of 600 nm and 140 nm,respectively,vertically grow on the surface of hollow microprism.Thanks to the NiCoP/Ni possess 3D complex structures.The hollow microprism as the frame structure can form an open,and connected channel to promote the transfer of electrolyte and the produced H₂ bubbles,and the nanoneedles growth on the surface of hollow microprism can provide large numbers of actives sites for HER.The electrochemistry tests show that the superaerophobic NiCoP/Ni electrocatalyst displays excellent HER performance,in which delivering a current density of 10,and 800 m A cm^-2 only required relatively low overpotentials of 26 and 205 m V.2.Fabricating Co/WO₂/NiW interfacial electrocatalysts for HERThe Co₃O₄nanowire precursor（Co₃O₄/Ni）was directly grown on the commercial nickel foam by using Co（NO₃）₂·6H₂O,CO（NH₂）₂ and NH₄F as metal ions.Then,the obtained Co₃O₄/Ni precursor was immersed in the mixed solution of nickel nitrate（Ni（NO₃）₂·6H₂O）and sodium tungstate（Na₂WO₄）through second hydrothermal reaction to attain NiWO₄/Co₃O₄ precursors.Finally,the Co/WO₂/NiW interfacial electrocatalyst was synthesized by annealing the NiWO₄/Co₃O₄ precursors in H₂/N₂ atmosphere.Furthermore,the Co/WO₂/Co W and WO₂/Co Cu electrocatalysts was also prepared with similar synthesis procedure.Electrochemistry test shows that the Co/WO₂/NiW,Co/WO₂/Co W,and WO₂/Co Cu electrocatalysts only required relatively low overpotential of 17 m V,26 m V and 39 m V,respectively to reach current density of 10m A cm^-2.Combining physical characteristy and electrochemistry test,The advantages of this kind of catalyst are as follows:（1）Co₃O₄ precursor is employed as the template for NiWO₄growth,which can provide a large specific surface area;（2）The metal Co core in the core-shell structure has good electrical conductivity and reduces the electron transfer resistance;（3）The in-situ WO₂interface with the alloy by hydrogen reduction method is conducive to the adsorption and desorption of the active H*,and the in-situ WO₂ can effectively reduce the hydrolysis ionization barrier,synergistic effect on HER,improving the bonding ability of the electrode surface to the active H*,and optimize the hydrogen adsorption free energy(△G_H*)of electrocatalyst.