Revealing the Dynamics of Platinum Nanoparticle Catalysts on Carbon in Oxygen and Water Using Environmental TEM

Abstract

Deactivation of supported metal nanoparticle catalysts, especially under relevant gas conditions, is a critical challenge for many technological applications, including heterogeneous catalysis, electrocatalysis, and fuel cells. It has been commonly realized that deactivation of catalysts stems from surface area loss due to particle coarsening; however, the mechanism for this remains largely unclear. Herein, we use aberration-corrected environmental transmission electron microscopy, at an atomic level, to observe in situ the dynamics of Pt catalysts under fuel cell relevant gas and temperature conditions. Particle migration and coalescence is observed to be the dominant coarsening process. In comparison with the case of H2O, O2 promotes Pt nanoparticle migration on the carbon surface. Surprisingly, coating Pt/carbon with a nanofilm of electrolyte (Nafion ionomer) leads to a faster migration of Pt in H2O than in O2, a consequence of a Nafion–carbon interface water “lubrication” effect. Atomically, the parti...