Identification of Iron Nanoparticles As Active Species for Oxygen Reduction in Non-Precious Metal Catalysts

Abstract

The widespread use of fuel cells is currently limited by the lack of efficient and cost-effective catalysts for the oxygen reduction reaction (ORR). Fe-based non-precious metal (NPM) catalysts exhibit promising activity and stability as an alternative to state-of-the-art Pt catalysts. However, the identity of the active species in NPM catalysts remains elusive, impeding the development of new catalysts. For the first time, we report the identification the catalytic species in an active NPM catalyst using Cl2 and H2 treatments to decrease heterogeneity. Additionally, we demonstrate the reversible deactivation and reactivation of the catalyst using the Cl2 and H2 treatments. Mössbauer and X-ray absorption spectra reveal that carbon-encapsulated Fe nanoparticles present in the as-prepared and H2-treated catalyst, but absent in the Cl2-treated catalyst are responsible for the observed ORR activity and stability of the catalyst. These findings suggest a new direction for the design and synthesis of enhanced NPM ORR catalysts.