Theoretical Calculation Of Typical Transition Metal Based ORR/HOR Catalysts For Fuel Cell

Hydrogen is the most important energy with the advantages of clean,affordable and sustainable.Fuel cells（FCs）are highly efficient devices for hydrogen utilization,in which cathode and anode take place oxygen reduction reaction（ORR）and hydrogen oxidation reaction（HOR）,respectively.However,Platinum-based materials as ORR/HOR catalysts with high-cost and limited resources hinder the commercialization of FCs.Then,Searching for low cost,high performance and stability catalysts for ORR/HOR is necessary to promote the commercialization of FCs.Transition metals（TMs）have great potential to replace precious metals and attracted more and more attention during the past decade due to their abundant reserves,low price and considerable ORR/HOR catalytic activity.To improve the activity and utilization of TM based catalysts,in this work,we fabricated TMs single-atom catalysts and alloy catalysts,and calculated their ORR and HOR activity by using density functional theory（DFT）.This work mainly includes the following two aspects:（1）The potential of 2D V₂CO₂ supported TM single-atom catalysts,including a series of 3d,4d and 5d metals,as ORR and HOR single-atom catalysts were investigated systematically by DFT.The binding energy and diffusion barrier of TM on V₂CO₂ find that 3d TMs are easier to anchor on V₂CO₂ surface,while 4d,5d TMs prefer doping on V₂CO₂ surface by replace one O atom.The majority of TM can form stable single-atom catalysts on V₂CO₂.The interaction and charge transfer between TM and V₂CO₂ can effectively regulate the electronic structure of TM and V₂CO₂,and then induce the TM as the efficient ORR active sites and O atoms as the major HOR active sites.The thermodynamic calculation of ORR and HOR indicates that,compared with pure Pt（111）,Sc-,Mn-,Rh-,Pt-V₂CO₂ show good ORR activity,and Sc-,Ti-,V-,Cr-,Mn-V₂CO₂ exhibit high HOR activity.Among them,Sc-V₂CO₂ can be the best candidate of bifunctional fuel cell catalysts with high catalytic activity,stability and low cost,and Mn-V₂CO₂ would become bifunctional ORR/HOR catalyst after improving its stability.（2）The HOR properties of TM（TM=3d,4d and 5d）and Cu near surface alloys were systematically calculated to search for TM HOR catalysts with high activity and stability.Firstly,ΔG_H*andΔG_OH*of TM（111）show that 3d TM（111）of IIIB-VIIB and Fe（111）exhibit too strong H and OH adsorption resulting in poor HOR activity and stability;3d TM（111）of IB,partial VIII and Ru（111）,Rh（111）,Os（111）have moderate H adsorption energy and too strong OH adsorption energy,showing poor anti-oxidation ability;Ag（111）and Au（111）bind H and OH too weakly with poor HOR activity;and Pt（111）,Pd（111）and Ir（111）have relatively suitable H adsorption and weak adsorption of OH displaying high HOR activity and oxidation resistance.Secondly,Cu（111）with acceptable HOR activity and poor oxidation resistance were selected as the representative of TM（111）to improve its anti-oxidation ability by constructing near surface alloy Cu/TM（111）with Cu as the surface.DFT calculations find that the adsorption strength of OH depends on the surface strain effect of Cu/TM（111）,compressive strain on Cu/TM（111）can weaken the OH adsorption and enhance the anti-oxidation ability of surface Cu.The HOR free energy and OH formation potential further confirms that Cu/Mn（111）and Cu/Co（111）would have high HOR activity and anti-oxidation ability,and show a great potential as HOR catalysts.