Screening the Performance of Silver Bimetallic Systems for the Oxygen Reduction Reaction in Alkaline Electrolyte

The large overpotential required for the oxygen reduction reaction (ORR) is a factor limiting the large-scale deployment of sustainable energy technologies (e.g. hydrogen fuel cells (H₂ FCs) and metal-air batteries). Consequently, developing better performing electrocatalysts for the ORR is one way to improve the energy efficiency and economic viability of these technologies. Currently commercialized proton exchange membrane H₂ FCs are limited to Pt-based catalysts due to the poor material stability of potentially active alternative non-platinum-based materials in acidic environments. In contrast, anion exchange membrane (AEM) FCs are an attractive alternative because of the wide array of promising and inexpensive catalysts materials that can be stabilized in alkaline environments. Ag-based catalysts are one exciting example of inexpensive alkaline-stable materials that have shown promising ORR selectivity, stability, and activity. Furthermore, we, and others, have shown that mixing Ag with other transition metals (e.g. Cu, Co, etc.), is an effective strategy for enhancement. Probing Ag-Cu bimetallics, specifically, we have previously clarified that the Ag matrix plays an important role in activity enhancement by tuning the electronic structure of the Cu-centered active site. Leveraging our fundamental understanding of Ag-based materials, in this work we discuss our progress towards describing how Ag interacts with other elements to yield specific properties that enhance activity and selectivity. By experimentally and computationally screening a series of bulk and surface Ag-bimetallic and intermetallic materials, Ag-M (where M = Pd, Cr, Mn, Fe, Ni, and Co), we characterize structure, miscibility, thermodynamic stability, and ORR activity and selectivity as a function of elemental composition. Using this work, we have setup a platform for comparing intrinsic ORR kinetics and selectivity to other material properties (composition, structure, etc.) and developed design strategies for enhancing the performance of Ag-based ORR catalysts.