Screening of Oxygen-Reduction-Reaction-Efficient Electrocatalysts Based on Ag-M (M = 3d, 4d, and 5d Transition Metals) Nanoalloys: A Density Functional Theory Study

Abstract

As a result of the high cost and scarcity of Pt and Pt-based materials as electrocatalysts with high oxygen reduction reaction (ORR) performance at the carbon-supported oxygen cathode of polymer electrolyte membrane fuel cells (PEMFCs), we perform a screening of ORR-efficient electrocatalysts based on Ag-M nanoalloys, where M is a 3d, 4d, or 5d transition metal using density functional theory (DFT) methods. We consider atomic oxygen adsorption energy Eads(O) as a descriptor to explore the cheap and ORR-efficient Ag-M(111) (M = 3d, 4d, and 5d transition metals) surfaces in various suballoying configurations compared to the Pt(111) surface. Our calculated results reveal that the Ag-shelled catalysts by subsurface alloying with all 3d, 4d, and 5d transition metals are more stable than pure Ag(111) by analyzing the surface energy and surface segregation energy of Ag-M alloys and consistent with Pt-M alloys suballoying with 3d transition metals. Moreover, the d-band center of the same Ag-M alloy with different suballoying configurations is found to be in the order of Ag-M skin < Ag-M subsurface < Ag3M mixing < pure Pt < Ag-M overlayer in Ag-shelled catalysts suballoying with all 3d, 4d, and 5d transition metals. We finally propose that Mn, Fe, and Co (3d), Zr, Mo, Nb and Ru and Ta and W (5d) are suitable catalysts for ORR on Ag3M mixing surfaces and Mn, Fe, and Co (3d) and Ta and W (5d) are suitable catalysts for ORR on Ag-M overlayer surfaces based on the fact that any catalyst with the strength of atomic oxygen reduction higher (but not very high) than that of pure Pt would be a suitable catalyst for enhanced ORR, which should be confirmed by further investigating ORR mechanisms on these catalyst surfaces in alkaline media both experimentally and theoretically. Moreover, the trends of oxygen reduction activity plotted against O binding energy, relative adsorption energies of ORR intermediates, and scaling relations between ORR intermediates (O, OH, and OOH) also stress our proposition illustrated above. Such a type of DFT investigation may open room for the researchers working in this direction.