Pt-free silver nanoalloy electrocatalysts for oxygen reduction reaction in alkaline media

The oxygen reduction reaction (ORR) plays a crucial role in electrochemical energy conversion and storage devices such as alkaline fuel cells and metal-air batteries. These systems, which could employ non-platinum catalysts for oxygen reduction, are cheaper and stable alternatives to their expensive counterparts like proton exchange membrane fuel cells (PEMFCs) working on platinum based catalysts. Various binary and ternary silver nanoalloys have been reported to act as efficient electrocatalysts for the ORR in alkaline fuel cells and batteries. Herein, we present a critical review on the recent advances made in silver nanoalloy electrocatalysts for the ORR in alkaline media. The mechanism of ORR on nanoalloys is described; the effect of structure and composition of various silver nanoalloys (including Ag-Cu, Ag-Pd, Ag-Au, Ag-Co etc.) on their ORR activity and stability is discussed. The rational design of electrocatalysts in order to maximize the number of catalytically active sites on the surface of the electrocatalysts for the ORR is also reviewed. Finally, we provide insights into the remaining challenges and directions for future perspectives and research.