Heterostructured Ni-based Catalyst Prepared By One-step Electrodeposition To Alkaline Hydrogen Evolution Performance

The exploitation of recyclable and green energy is a hopeful strategy with bright prospects to retard the dependence of fossil fuel resources or even take the place of conventional energy sources.Green energy such as nuclear energy,wind energy,water energy,solar energy,and hydrogen energy,have gradually entered people’s visions.And the unstable electricity produced by wind energy and solar energy could be transformed into hydrogen energy with high energy density through cheap and efficient water electrolytic technology.For the industrialization of water electrolysis hydrogen production technology,it is very important to design and prepare high-efficiency and low-cost alkaline HER catalysts.However,the kinetics of the HER in alkaline medium is slow relative to that in acid because of the additional decomposion of extra water molecules to obtain the active H^*.The heterostructure catalyst provides active functional reaction sites for the entire HER reaction due to the synergetic effect at the interfaces,and has unlimited potential in the field of alkaline HER catalysis.Construction of heterostructure with synergetic effect is an effective activation strategy for hydrogen evolution reaction,whereas it often requires treatment of high temperature and high pressure for decade hours.Based on the above problems,we propose a one-step electrodeposition method to prepare the heterostructured Co Ni-LDH@Ni Co alloy catalyst with a highly alkaline HER performance.The main research contents and conclusions are as follows:（1）combination of the diffusion limited cluster aggregation model（DLCA）and the nucleation limited aggregation model（NLA）,we explore the fractal growth mechanism of kinetic controlled dendritic Ni-based alloys in the far equilibrium state.The effects of deposition current density and deposition time on the fractal growth of dendritic Ni Co Mo alloys are explored respectively,and the fractal growth paths in the process of electrodeposition of dendritic Ni-based alloys are proposed,which are smooth deposition,in-situ deposition and defect deposition.It provides suitable electrochemical deposition conditions,a higher deposition current density(-0.3A·cm^-2)and deposition time（100 s）,for the subsequent preparation of a one-step electrodeposition of heterostructured Co Ni-LDH@Ni Co alloy catalyst with wheat ear-like Ni Co alloy of fractal characteristics.（2）The heterostructured Co Ni-LDH@Ni Co alloy catalyst combining a wheat ear-like Ni Co alloy with fractal characteristics and amorphous Co Ni-LDH was prepared by a one-step electrodeposition method.Taking advantage of the high deposition current density,the reduction of metal ions and electrode polarization occur together.The negative shift of the cathode electrode potential causes the reduction of oxyacid radicals（NO₃^-）in the electrolyte to occur,and the OH^-generated increases the local p H.The p H value further promotes the production of Co Ni-LDH.Adjusting the ratio and distribution of Co Ni-LDH and Ni Co alloy in the heterostructure catalyst by adjusting the molar ratio of metal ions to NO₃^-in the electrolyte（MC/N-1:0、MC/N-1:0.5、MC/N-1:1 and MC/N-1:2）,the heterostructured Co Ni-LDH@Ni Co alloy catalyst with excellent HER catalytic performance was obtained（MC/N-1:0.5）,presented enhanced alkaline HER activity,achieved current densities of 10 m A·cm^-2 at quite low overpotential of 69 m V,improved 60%forη₁₀ by comparing with the pristine Ni Co alloy,and excellent exchange current density up to 2.38 m A·cm^-2.（3）The heterostructured Co Ni-LDH@Ni Co alloy catalyst benefits from the high specific surface area and large exposure active sites of porous spheres composed of fractal wheat-like Ni Co alloy and amorphous Co Ni-LDH nanosheets.And the synergetic effect at the interface of Co Ni-LDH and Ni Co alloy accelerates the adsorption and dissociation of water molecules under alkaline conditions,thereby accelerating the decisive step of Volmer reaction,realizing the catalytic purpose of heterostructure catalyst 1+1>2,and improving alkaline HER catalytic performance.This work provides some directions and inspirations for exploring the simple preparation method of heterostructured oxygen/hydroxide@alloy catalyst and the corresponding interfacial synergetic effect mechanism.