In Situ Stability Studies of Platinum Nanoparticles Supported on Ruthenium-Titanium Mixed Oxide (RTO) for Fuel Cell Cathodes

Using a variety of in situ techniques, we tracked the structural stability and concomitantly the electrocatalytic oxygen reduction reaction (ORR) of platinum nanoparticles on ruthenium-titanium mixed oxide (RTO) supports during electrochemical accelerated stress tests, mimicking fuel cell operating conditions. High-energy X-ray diffraction (HE-XRD) offered insights in the evolution of the morphology and structure of RTO-supported Pt nanoparticles during potential cycling. The changes of the atomic composition were tracked in situ using scanning flow cell measurements coupled to inductively coupled plasma mass spectrometry (SFC-ICP-MS). We excluded Pt agglomeration, particle growth, dissolution, or detachment as cause for the observed losses in catalytic ORR activity. Instead, we argue that Pt surface poisoning is the most likely cause of the observed catalytic rate decrease. Data suggest that the gradual growth of a thin oxide layer on the Pt nanoparticles due to strong metal-support interaction (SMSI) is the most plausible reason for the suppressed catalytic activity. We discuss the implications of the identified catalyst degradation pathway, which appear to be specific for oxide supports. Our conclusions offer previously unaddressed aspects related to oxide-supported metal particle electrocatalysts frequently deployed in fuel cells, electrolyzers, or metal-air batteries.