(Invited) Understanding the Degradation of Nanocatalysts in PEM Fuel Cells By Identical Location Aberration-Corrected TEM/STEM

Abstract

A thorough knowledge of the atomic structure and composition of catalyst nanoparticles is paramount to the development of advanced materials for proton exchange membrane fuel cells (PEMFC), one of the most promising energy conversion devices for automotive and stationary applications. Pt and Pt-based alloys nanoparticles (NPs) are currently used as the catalyst to promote the kinetics of the hydrogen oxidation and oxygen reduction reactions in the anode and cathode of the fuel cell, respectively. Yet, the durability of the catalysts remains the main issue for their commercialization.In this talk, the focus is to understand the behavior of Pt and Pt-alloy NPs during the various stages of fuel cell cycling. For this purpose a set-up was developed to simulate the effect of voltage cycling on the cathode side of the fuel cell. In this set up, catalyst NPs supported on carbon nanotubes and amorphous carbon were deposited on a gold TEM grid attached to a gold plate, which is used as a working electrode in a three electrode electrochemical cell. The NPs were then observed by advanced transmission electron microscopy, before and after cycling. The experiments show particle migration in conjunction with carbon corrosion during the initial cycles, whereas the appearance of single atoms and atomic clusters on the surface of the carbon support appear after additional voltage cycling as a result of surface dissolution of NPs. For the case of alloyed NPs, the experiments show a heterogeneous deposition of Pt on the NPs. Keywords: Catalysts, Nanoparticles, Proton Exchange Membrane Fuel Cells, Aberration-corrected TEM/STEM, Tomography, Identical Location TEM.