In Situ Liquid Cell TEM Study of Morphological Evolution and Degradation of Pt-Fe Nanocatalysts During Potential Cycling

Nanocatalyst degradation is a serious limiting factor for the commercialization of proton exchange membrane fuel cells. Although the degradation has been extensively studied in the past through various ex situ electrochemical methods, employing an in situ technique can greatly improve our understanding of the mechanisms involved during the electrochemical cycling. In this work, we have employed an in situ liquid cell inside a TEM for a simultaneous investigation of the structural evolution and electrochemical response of Pt-Fe nanocatalysts. We demonstrate that the coarsening processes of these nanocatalyst particles, including the nucleation and growth, are not uniform, both in space and in time scale. The growth rate is found to be both site- and potential-dependent. Furthermore, these particles were found to exhibit considerably different behaviors when attached to an electrode as opposed to when isolated in the electrolyte. With Pt-Fe nanoalloy system as a candidate material, this work demonstrates that the in situ structural characterization of nanocatalysts under electrochemical bias and inside the native electrolyte environment provides much deeper insight into the catalyst degradation mechanisms as compared to the routine ex situ electrochemical studies.