Silver Oxygen Reduction Electrocatalyst in Alkaline Medium: Aging and Protective Coating

The oxygen reduction reaction (ORR) is a key process in anion exchange membrane fuel cells. The alkaline conditions should allow silver-based cost-efficient catalysts to replace platinum group metal materials. However, Ag electrochemical stability or lack of stability in alkaline medium is still to be demonstrated. Herein, Ag catalyst nanoparticles (NPs) are characterized by identical location transmission electron microscopy and X-ray photoelectron spectroscopy after electrochemical cycling, revealing the losses of activity and surface. Herein, a facile method for enhancing the chemical stability of Ag catalysts in an alkaline environment by depositing a protective polydopamine (PDA) coating is reported. It is enhanced via crosslinking with polyethyleneimine (PEI), on the surface of Ag NPs. The enhanced electrochemical stability of Ag PDA–PEI nanocatalyst via the analysis of ORR polarization curves during accelerated stress test cycling is demonstrated, with at least one order of magnitude higher durability than the standard Pt/C catalyst. Moreover, electrochemical measurements indicate that the protective PDA–PEI coating has good permeability to O₂, with a positive effect on the ORR activity of Ag NPs.