First-Principles Study On Transtion Metal Borides For Catalytic Water Decomposition

With the rapid development of technology and industry,mankind is facing problems of environmental pollution and energy shortage.As a clean energy source,hydrogen is therefore gradually being taken seriously by researchers.To achieve hydrogen production from clean energy sources,electrochemical and photoelectrochemical hydrolysis is a favourable strategy to benefit from abundant water resources and provide high purity hydrogen production.Currently,Pt is the most efficient electrocatalyst for hydrogen precipitation reactions(HER)with an overpotential close to zero,while Ir O₂ and RuO₂ are considered to be benchmarks for oxygen absorption reaction(OER)electrocatalysts.However,the scarcity and high cost of these precious metal-based electrocatalysts greatly hinder their large-scale application in commercial electrolysers.Transition metal borides(TMBs)exhibit excellent electrocatalytic activity due to their unique staggered arrangement structure and bonding properties.In this work,the potential of bulk phase nickel borides(Ni₂B)and(two-dimensional transition metal borides MBenes)for the electrolysis of water for hydrogen and oxygen production has been investigated using a computational approach based on first principles of density general function theory using the Vienna Ab initio Simulation Package(VASP)computational package.Details of the work are shown below.(1)The HER electrocatalytic activity of nickel boride(Ni₂B)was first investigated.It was found that Ni₂B is structurally stable and has good electrical conductivity.the HER activity of the Ni₂B-B surface is higher than that of the Ni₂B-Ni surface,and the Gibbs free energy of adsorption(GH)is close to zero,showing good electrocatalytic activity.Single-atom substitution doping of Ni atoms on the surface was carried out using the isoperiodic transition metals M(Co,Cr,Fe and Mn).The results showed that the doping improved the HER catalytic activity of the Ni₂B-Ni surface.(2)To investigate its feasibility as a HER/OER bifunctional electrocatalyst for total water resolution,the OER catalytic performance of the Ni₂B(001)crystalline surface was also investigated in relation to this.It was found that the Ni₂B-Ni surface has better OER performance.The OER performance of the Ni₂B-Ni surface was greatly enhanced after doping,and the OER activity of the Ni₂B-B surface was reduced.The results predict that Ni₂B is a good non-precious metal HER/OER bifunctional catalyst.(3)In this work,density flooding theory was used as the research method to select six typical first transition metal elements to construct MBenes models(M=Co,Cr,Fe,Mn,V and Ni)and to study their HER and OER performance.The study calculations show that among the six MBenes,Co₂B₂,Cr₂B₂ and Fe₂B₂ have excellent HER reactivity and Ni₂B₂ exhibits good OER reactivity.The results predict that MBenes are good HER and OER electrocatalyst.