Impedance Spectroscopy Studies of Oxygen Reduction Reaction on Thin Film Platinum Microelectrodes Supported on YSZ

Abstract

Platinum is considered a promising electrocatalyst in solid oxide fuel cells (SOFCs) for micro and portable applications. Although the platinum/YSZ system has been studied extensively, numerous open questions remain with regard to the oxygen reduction reaction (ORR) mechanism at the molecular level. It has been proposed that limiting reaction steps may include dissociative adsorption of oxygen, surface diffusion of oxygen species and migration of oxygen species to the electrolyte (charge transfer) through the three-phase boundaries. In this study, dense platinum microelectrodes with well-defined geometries were prepared by microfabrication techniques and patterned using photolithography. Electrochemical impedance spectroscopy (EIS) of Pt microelectrodes is conducted at pO2 levels between 0.001kPa to 100kPa and temperatures between 570{degree sign}C-750{degree sign}C. The EIS response could be modeled using a Gerischer impedance element below 700{degree sign}C. It is proposed that oxygen adsorption and surface diffusion simultaneously act as rate-limiting (co-limiting) processes of ORR in the temperature and pO2 range examined.