Oxygen Reduction Characteristics on Ag, Pt, and Ag-Pt Alloys in Low-Temperature SOFCs

Abstract

Oxygen reduction reactions on Pt, Ag, and Pt-Ag alloys were investigated at temperatures between 300oC and 500oC with the help of electrochemical impedance spectroscopy. The rate-determining step in oxygen reduction reactions was found to depend on the choice of material as well as porosity and thickness. On 600nm dense Ag, dissociative adsorption/reduction of oxygen was dominant. On porous Pt charge transfer reaction in the vicinity of triple phase boundary is rate determining. Slow oxygen diffusion was rate dominant with 600nm dense Ag3Pt. I-V characterization was also performed at 350oC on fuel cells consisting of different metal cathodes. Silver-based alloys were found not suitable as cathodic catalysts for low temperature solid oxide fuel cells due to formation of silver oxide, in turn leading to a rapid decline in voltage with increasing current densities. Among the investigated metals, thin porous Pt was identified as the best cathode.