In Situ Growth Of NiFe-based LDH On Reduced Graphene Oxide Modified Nickel Foam And Their Electrolysis Performance For Overall Water Splitting

The increasing depletion of fossil energy forces people to make continuous efforts to develop new renewable energy sources.The hydrogen production process by water splitting has the advantages of high efficiency,simple processing and pollution-free production,thus being considered to have a promising development prospect.However,Pt-based electrocatalyst,the most commonly used one at present,is seriously suffered from low reserves and high cost,so the development of non-noble metal catalyst for hydrogen production by highly efficient water splitting has become the focus of research.In this paper,Ni Fe-based-LDH/r GO/NF composite electrocatalysts were prepared by two-step hydrothermal method using nickel foam with excellent electrical conductivity as the substrate,and the performance for oxygen evolution reaction（OER）,hydrogen evolution reaction（HER）and overall water splitting were studied.The main results are as follows:1.Firstly,the reduced graphene oxide（r GO）modified nickel foam（NF）was obtained by hydrothermal method,then Ni Fe LDH was in situ grown on r GO/NF by hydrothermal step using urea as precipitant to obtain a series of Ni_xFe₁-LDH/r GO/NF（x=3,2,1）composite electrocatalysts.The Ni_xFe₁-LDH nanosheets（～190-750×20-80 nm）were vertically staggered on r GO/NF substrate and exhibit nanosheets array-like morphology with abundant open pore channels.The Ni₂Fe₁-LDH/r GO/NF showed optimal electrocatalytic performance for OER and HER in alkaline solution（1 M KOH）,which only require 228 and 109 m V at 10 m A cm^-2,respectively,and the Tafel slopes are only 37.9 and 121 m V·dec^-1,respectively.When used as both cathode and anode,Ni₂Fe₁-LDH/r GO/NF only requires 1.62 V for overall water splitting.Meantime,the catalyst has excellent long-term stability.The results can be attributed to the smaller nanosheets（～626×37.5 nm）,abundant exposed active sites and larger electrode-electrolyte contact area along with Ni-Fe electronic modification and the LDH-r GO/NF synergistic effect.2.Nanosheets array-like ternary LDH composite electrocatalysts Ni_xCo_2-xFe₁-LDH/r GO/NF（x=1.5,1,0.5）were prepared by doping the third transition metal cobalt to the LDH layer lattice.The overpotentials of Ni_1.0Co_1.0Fe₁-LDH/r GO/NF in 1 M KOH for OER and HER are only 215and 106 m V at 10 m A cm^-2,respectively,and the Tafel slopes are as low as28.6 and 99.8 m V dec^-1,respectively.The decomposition voltage is only1.57 V for overall water splitting,better than Ni₂Fe₁-LDH/r GO/NF composite.The results can be explained as the more accessible active sites provided by the smaller and thinner size of Ni_1.0Co_1.0Fe₁-LDH nanosheets（～525×16 nm）,further electronic modification by Co species and synergistic effect between Ni_1.0Co_1.0Fe₁-LDH and r GO/NF.The nanosheets array-like morphology matrix-based LDH/r GO/NF composite electrocatalysts and their catalytic performance regularities in the present work provide new ideas for the development of better multi-component materials for hydrogen production by electrolysis of water.