First-principles Investigation Of PtCu As A Catalystfor The Oxygen Reduction Reaction

In the process of the rapid development of human society,energy and environmental issues have attracted widespread attention.People have paid more and more attention to the development of low-carbon energy technologies and sustainable development of new energy.Proton exchange membrane fuel cell（PEMFC）has been used in many fields as a green energy source with the most development prospects due to its excellent performance in various aspects such as high energy density and fast refueling.Pure platinum（Pt）and Pt-based catalytic materials are still the most effective electrocatalysts in fuel cells,but their high cost and slow kinetics of the oxygen reduction reaction（ORR）at the cathode are the two main disadvantages,so developing high-efficiency,low-cost electrocatalysts is still a key scientific issue in the development of PEMFC.In recent decades,many studies have shown that doping other metals on the basis of pure Pt to form binary or ternary alloys will enhance the activity of the catalyst and reduce the cost of the catalyst,which has led people to realize the use of intermetallics.The synergistic effect of the catalyst can improve the performance of the catalyst and provide a new idea for the development of the catalyst,but the microscopic mechanism of the catalyst at the atomic level is not very clear,and some experimental phenomena cannot be reasonably explained.In this paper,first-principles methods are used to study the structure and properties of the surface of Pt and PtCu alloys.The most stable adsorption structure of small molecular intermediates is identified.Three possible reaction paths of ORR are discussed.The free energy of the catalyst is analyzed.The reasons for the enhanced activity of PtCu alloy catalyst were elucidated from kinetics and thermodynamics,which provides a certain theoretical guidance for the design and development of new catalysts.The main contents of this article are as follows:（1）The density functional（DFT）method was used to systematically study the ORR mechanism of Pt（111）surface.Firstly,the adsorption energy values of seven kinds of small-molecule adsorbents at different sites on the surface of Pt（111）were calculated,and the most stable adsorption sites were determined.Secondly,the possible reaction path of ORR was studied,and the results were obtained on Pt（111）ORR is more inclined to take the OOH dissociation path,that is,₍2(6（9）→₍(6（9）→₍(6（9）→₍(6（9）→₂₍(6（9）,which is consistent with the previous results.The speed-determining step is the O protonation step,and the energy barrier of the speed-determining step is 1.10e V,finally,the Gibbs free energy diagram is plotted,and the overpotentialηis 0.52e V.（2）The DFT method was used to systematically study the ORR mechanism of the Pt/PtCu₃（111）surface and compare it with the Pt（111）surface.It was found that the adsorption sites of small molecules on this catalyst are similar to Pt（111）,and the adsorption energy is lower.In terms of kinetics,the ORR of the Pt/PtCu₃（111）catalyst is more inclined to take the H₂O₂ dissociation path,that is,₍2(6（9）→₍(6（9）→_22ad→₍(6（9）→₂₍(6（9）,and the speed-determining step is H₂O₂ dissociation.In this process,the maximum energy barrier is 0.62e V,and the thermodynamically derivedηis 0.48e V,which is lower than that on the surface of Pt（111）,which explains to some extent why the activity of the Pt/PtCu₃（111）catalyst is improved.（3）The ORR mechanism of the ternary catalyst PtCu Ag（111）surface was systematically studied by density functional method,Similar to the previous one,the ORR mechanism on the surface of ternary catalyst PtCu Ag（111）was systematically studied to investigate the influence of components on the performance of catalyst.