Construction Of Hierarchical Structure Based On Transition Metal Oxide And Its Electrocatalysis For Water Splitting

Due to the excessive use of traditional energy sources,environmental problems such as environmental pollution and energy crisis have brought about global problems that need to be solved.Therefore,the development and utilization of clean renewable energy sources has attracted more and more researchers' attention.The development and use of electrocatalysts to catalyze water splitting is one of the most effective ways to convert electrical energy into clean,sustainable chemical energy.The efficiency of electrocatalytic decomposition of water is directly related to the performance of catalyst materials.At present,most precious metal-based materials(such as Pt,IrO2,etc.)are used as high-efficiency catalyst for water splitting.However,due to the high cost of precious metals and their rare reserves,designing and preparing efficient,stable and inexpensive non-precious metal-based electrocatalyst has become the key to further development of electrolysis water hydrogen production technology.On the one hand,this paper works aim to build a transition metal oxide based nanostructure to improve the efficiency of electrode-loaded active materials,optimize the charge transport pathway,and fully expose the active sites;on the other hand,by introducing other transition metal elements,constructing bimetal/trimetal oxide composite material to optimizes its electronic structure and promotes the adsorption and dissociation of the participating reactants on the surface.The synergistic effect of nanostructure construction and interface component regulation is used to increase the catalytic rate of hydrogen evolution,oxygen evolution and water decomposition reactionThe specific work is as following:(1)Construction of NiFe2O4/Ni(OH)2 three-dimensional hierarchical structure on nickel surface and its electrocatalytic water oxidation performance:The porous nickel foam electrode is in-situ activated by a cationic assisted etching method.In the process of hydrothermally corroding the surface of foamed nickel,a trivalent Fe3+ ion precursor was added,and under the auxiliary activation of Fe3+,the structural components of the surface of the foamed nickel were obtained by changing the reaction conditioins,thereby obtaining NiFe2O4/Ni(OH)2 composite electrode with three-dimensional porous nanostructures.The further structural characterization indicates that the NiFe2O4/Ni(OH)2 multi-level nanostructures exhibit good interfacial contact.Interestingly,the construction of this NiFe bimetal oxide composite effectively changed the reaction path in the catalytic water oxidation reaction.The reaction path is converted to a two-electron H2O2 oxidation step.This transformation of the reaction path effectively accelerates the rate of surface reactions.In a 1.0 M KOH alkaline electrolyte,the OER Tafel slope is only 25 mV dec'1,and the oxygen evolution at a current density of 10 mA cm-2 only need a overpotential of 129 mV,showing excellent water oxidation catalytic activity.(2)Construction of NixCo1-xoO4@CoMoO4 Multi-level Nano-brush Array and Its Electrocatalytic Water Splitting:The porous nickel foam surface is activated by deionized water hydrothermal etching to obtain surface-modified activated nickel foam.Based on the above activated foamed nickel,a NixCo1-xMoO4@CoMoO4 hierarchical array was constructed,compared to the normal nanorod array obtained by growing CoMoO4 directly on the nickel foam,the NixCo1-xMoO4@CoMoO4 hierarchical structure consisted of vertically growing one-dimensional CoMoO4 nanorods.The two-dimensional ultra-thin NixCo1-xMoO4 nanosheets are grown together.In this way,the 1D nanorods ensure charge transfer inside the electrode and provide structural support for the hierarchical structure,and the 2D nanosheets enhance radial charge transfer and further manufacture and expose more active sites.Therefore,the material exhibits excellent HER,OER and total water splitting activity.In a 1.0 M KOH alkaline electrolyte,the overpotential(?10)of HER and OER is only 61 and 180 mV,respectively.Moreover,the composite electrode only needs 1.46 V to reach a current density of 10 mA cm-2 and remains stable for more than 30,000 s,exceeding most of the currently reported transition metal-based electrocatalysts.