Design Of Transition Metal-based Catalyst And Its Electrocatalytic Performance For Water Decomposition

Since the 21st century,the energy issue has attracted global attention,and people’s demand for green and renewable energy is growing day by day.There are many ways to get clean energy such as solar power,tidal power and wind power.However,some of the methods mentioned above are random and intermittent,which makes it is difficult to meet the higher demand for clean energy.The technology of electrochemically catalyzed water decomposition to produce hydrogen energy has a wide range of raw materials,high Faraday efficiency and pollution-free products,so it has great potential to meet this demand.The technology of chemically catalyzed water decomposition to produce hydrogen energy not only has high efficiency and zero carbon emission,but also is expected to achieve large-scale marketing.It is a research hotspot in the field of hydrogen energy.Although the electrochemical water decomposition technology has many advantages,it also faces some problems and challenges to be solved.Theoretically,water decomposition requires a voltage of 1.23 V.However,in fact,both the hydrogen evolution reaction at the cathode and the oxygen evolution reaction at the anode have high reaction energy barrier,concentration polarization overpotential between the electrode and the solution,and the resistance of the solution itself.At present,in the field of electrolytic water,although the noble metals and their oxides such as Pt,Ru O₂and Ir O₂have excellent catalytic performance as electrochemical catalysts in hydrogen evolution or oxygen evolution reactions,these precious metals have shortcomings such as scarce resources,high price and poor durability,so it is difficult to be widely used.Therefore,over the past few decades,researchers have worked hard to design non-precious metal electrochemical catalysts with high performance.Such as transition metal phosphates,sulfides,selenides,carbides,and oxides have been reported as promising electrochemical catalysts for HER or OER.Most of the catalysts studied at present are only active in HER or OER half-reaction,and few catalysts have excellent catalytic activity in both HER and OER under the same p H condition.Therefore,it is of great significance to find a bifunctional electrocatalyst with high efficiency,low cost and abundant raw materials for the overall water decomposition.Based on the above,we designed two catalyst materials for electrochemical catalysis of total water decomposition.（1）A novel ultra-thin nanosheet coated three-dimensional nanoflower structure（Ni₃S₂-Ni_xP_y/NF@Ni Fe LDH）was successfully synthesized on nickel foam（NF）by hydrothermal,phosphating and electrodeposition methods.First,a simple hydrothermal process was used to vulcanize NF into Ni₃S₂sheet structure as substrate to provide a larger surface area and stable support for subsequent growth.Then,the nanosheets were aggregated into nanoflowers by phosphating,and the heterogeneous structures of Ni₃S₂-Ni_xP_ywere formed.Finally,ultrathin Ni Fe LDH nanosheets are uniformly plated on the surface of the nanoflowers.After electrochemical performance test,Ni₃S₂-Ni_xP_y/NF@Ni Fe LDH catalyst showed very low OER overpotential of 248 and 298 m V at 50 and 100 m A cm^-2,and low HER overpotential of 137 m V at 10 m A cm^-2.At the same time,Ni₃S₂-Ni_xP_y/NF@Ni Fe LDH is used as a cathode anode catalyst for overall water splitting testing,a current density of 10 m A cm-2 can be achieved with only 1.54 V overpotential.（2）We successfully synthesized V-NF@Ni Mo O₄/Ni₁₂P₅spherical net crosslinked composite catalyst by two-step hydrothermal method and one-step phosphating method.The material was tested for OER performance.Only 254 and 333 m V of overpotential could reach 50 and 100 m A cm^-2current density.In HER performance test,only 161 and 241 m V overpotential can reach 10 and 20 m A cm^-2current density.When V-NF@Ni Mo O₄/Ni₁₂P₅was used as catalyst for the cathode and anode in the total water decomposition test,only 1.43 V overpotential could reach the current density of 10 m A cm^-2.In addition,the material has long cycle stability of 55 h.