Structural Dynamics of Nanoalloy Catalysts Inside Fuel Cells by In Operando High-Energy X-Ray Diffraction

Nanoalloy catalysts for proton exchange membrane fuel cells (PMFCs) undergo large atomic-level changes during electrochemical reactions, including changes in the chemical composition, particle size and atomic ordering. The dynamics of the changes and their impact on the cell performance, however, are not well understood. This is largely because they are studied on model catalysts under laboratory conditions. We will present results from recent high-energy x-ray diffraction (XRD) studies [1-4] on the dynamic behavior of metallic nanoalloy catalysts inside an operating PEMFC. Results show that the changes are most intense in the first hour of the cell operation, turning incremental but still significant during further cell operation. The electrocatalytic activity of the nanoalloys also changes, as reflected by the PEMFC current output. We will also show that the rate and magnitude of the changes may be rationalized when the limits of traditional relationships used to connect the composition and structure of nanoalloys with their activity and stability, such as Vegard’s law, are recognized. The new insight into the actual evolution of nanoalloy catalysts for PEMFCs is likely to inspire new efforts to improve their activity and stability under operating conditions.<br/><br/><i>V. Petkov et al. Nano Energy 49, 209 (2018).</i><br/><i>V. Petkov et al. Nanoscale </i>11, 5512 (2019).<br/><i>Zh. Kong et al. J. Am. Chem. Soc. </i>142, 1287 (2020).<br/>Z. –P. Wu et al. <i>Nature Commun. </i>12, 8597 (2021)