Dynamics of an Oxide Fuel Cell Catalyst Revealed by Operando X-Ray Scattering

Furthering understanding of the catalytic mechanism in the oxygen reduction reaction (ORR) is critical to advancing and enabling fuel cell technology. In this work, we use operando synchrotron diffraction and resonant elastic X-ray scattering (REXS) to investigate the interplay between the structure and oxidation state of a Co-Mn oxide catalyst, which shows an impressive ORR activity in alkaline fuel cells. REXS was used to simultaneously observe the dynamic changes in the structure and valence state of both Co and Mn under steady state (constant applied potential) and non-steady state (cyclic voltammetry). Under steady-state conditions, an irreversible structural phase change is observed at low potentials, along with an accompanying reduction in both Co and Mn valence. With fast diffraction data collection enabled by a synchrotron source, we resolved periodic changes in the lattice parameter aligned with the cyclically applied potential. When cycled through low potentials, the catalyst exhibited a reversible rapid increase in strain. Through this work, we gained a greater understanding of the ORR mechanism in Co-Mn oxide catalysts and demonstrated the unique capabilities of combining structural and chemical characterization in REXS.