Design and synthesis of degradation-resistant core–shell catalysts for proton exchange membrane fuel cells

Abstract

Core@shell catalysts supported on carbon with Ag core and Pt shell were synthesized by a chemical process. EDX spectra confirmed the formation of Ag@Pt core–shell catalysts. High resolution transmission electron microscopy (HRTEM) revealed that the Pt-shell was epitaxially matched to the Ag core. Electrochemical tests on proton exchange membrane (PEM) fuel cells made with Ag@Pt core–shell catalysts as cathode exhibited comparable performance to cells made using commercial Pt–Co-based catalysts as cathodes. Theoretical work suggested that Ag@Pt catalysts should be more stable in the PEMFC applications compared to monolithic Pt catalysts because Pt shell in Ag@Pt catalysts exhibits lower chemical potential of Pt than in monolithic Pt catalysts, thus reducing tendency for dissolution and Ostwald ripening. Lower chemical potential of Pt in the shell is attributed to larger lattice parameter of Ag compared to Pt, which puts the Pt shell in biaxial tension or reduced biaxial compression as compared to monolithic Pt catalysts. Preliminary out-of-cell tests show Ag@Pt catalysts to be stable in an environment containing ionic platinum.