First-principles Study On Electrochemical Performance Of Ruthenium-based Alloy Material

With the development of the economy,global energy structure and environmental issues have attracted increasing attention.People urgently need to develop more clean and renewable energy sources to reduce greenhouse gas CO₂ emissions and environmental pollution.Electrochemical water splitting to generate hydrogen by using renewable energy has attracted more and more attention.The development of stable and efficient electrocatalysts for electrochemical hydrogen evolution reaction（HER）or electrochemical oxygen evolution reaction（OER）has attracted more attention.Noble metal catalysts still the most active catalysts for HER and OER in a wide p H range（for example,Pt catalysts used in HER,Ir O₂/Ru O₂ catalysts used in OER）.Noble metal-based electrocatalysts are still the most promising series for OER and HER,and the reduction of catalyst cost through alloying has attracted more and more attention.In recent years,more and more people pay attention to theoretical calculations,which can not only explain some unexplainable mechanism problems in experiments.Moreover,theoretical simulation can predict the feasibility of materials in a shorter time and at lower cost,and the rationality of the research method saved a lot of time and cost for the experiment,and has certain research guiding significance.The author uses a combination of computer simulation and experiment to study the structure and electrocatalytic properties of ruthenium-based alloys.The geometric structure,electronic structure and electrocatalytic mechanism of ruthenium and copper,nickel,cobalt and other transition metal composite alloy materials were calculated by DFT.The specific work content is as follows:（1）Construct a binary alloy with metals Cu and Ru as the HER catalyst.Applying first-principles calculations based on DFT,the formation energy of binary alloys with different ratios（Cu:Ru=1:2,1:1,and 2:1）was calculated to analyze their structural stability.It is found that Cu₂Ru（101）,Cu Ru（101）and Cu Ru₂（100）were the most stable and easy to obtain.Five possible adsorption sites(T_Ru,T_Cu,B_Ru-Ru,B_Cu-Cu,B_Cu-Ru)were selected to combine with H atoms,among which the B_Cu-Ru site was proved to be the best adsorption site for HER.By analyzing the Gibbs free energy of HER,It was believed that Cu Ru was a suitable catalyst(ΔG_H*=-0.10 e V).The”volcano map”showed that the Cu Ru alloy was close to the peak of the volcano map and its potential HER activity.Prove the feasibility of theoretical research through experimental observation.The Cu Ru alloy was prepared by a simple liquid-phase reduction method,and current density of 10 m A·cm^-2 could be reached at a low overpotential of 86.7 m V in 0.1 M KOH solution,and the corresponding Tafel slope was as small as 40 m V·dec^-1.The electrochemical double-layer capacitance was 46.1 m F·cm^-1,and the electrochemically active surface area（ECSA）of the electrode is 1152.5 cm².Cu Ru alloy was an excellent hydrogen evolution catalyst.This work will help develop ultrafine alloy catalysts for energy conversion.（2）The binary alloy was constructed with metal Ni and Ru,which was used as OER catalyst.Through first-principles calculations based on DFT,the structural stability and catalytic performance of binary alloys with different ratios（Ni:Ru=1:2,1:1,and 2:1）are studied.Facts have proved that Ni Ru（111）surface was the most stable and easiest to obtain.The charge distribution on the surface found that electrons were enriched near nickel atoms,and electrons were vacant near ruthenium atoms.Three possible adsorption sites(T_Ru,T_Ni,H_Ni-Ru)on the alloy surface were selected to combine with different oxygen-containing functional groups,among which H_Ni-Rusite proved to be the best adsorption site for OER.At the same time,it was found that the conversion from^*O to^*OOH was the rate-determining step.By analyzing the Gibbs free energy of OER on the alloy surface,it could be considered that Ni Ru was the best catalyst.The Gibbs free energy was 1.83e V（η=0.60V）.It could provide ideas for experimental research on alloy electrocatalysts.（3）A ternary alloy was constructed with metals Ni,Co and Ru as an electrocatalyst.Through first-principles calculations based on DFT,the structural stability,conductivity and electrochemistry of alloys with different ratios（Ni:Co:Ru=1:2:3,2:1:3 and 3:3:6）performance were study.Facts have proved that Ni Co₂Ru₃（111）,Ni₂Co₁Ru₃（111）,Ni₃Co₃Ru₆（111）planes are the most stable and easiest to obtain among several crystal planes.The best adsorption site on the alloy surface was selected to combine with H atoms,which Co-Ru sites were proved to be the most likely adsorption sites for HER.and Ni Co₂Ru₃ was the best hydrogen evolution ratio.By analyzing the Gibbs free energy of HER on the alloy surface,it was considered that Ni Co₂Ru₃ was a suitable catalyst(ΔG_H*=-0.10e V).The oxygen evolution reaction was studied on the surface of alloy models with different proportions,and its mechanism was studied step by step.It was found that Ni Co₂Ru₃also had excellent OER activity（η=0.67V）.Ni Co₂Ru₃ alloy was an excellent hydrogen and oxygen evolution catalyst.This work will help to develop bifunctional electrolytic water catalysts for alloys.