Platinum Catalyst Degradation: Unusual Nucleation and Growth of Nanoislands

Abstract

The longevity of a catalyst plays a crucial role for many industrial scale applications. Platinum is the best candidate to be used in electrochemical energy conversion systems due to its high activity. However, platinum catalysts degrade during fuel cell operation. The origin of this degradation, the loss of material, is very likely rooted in the roughening of the surface: the nucleation and growth of nanoislands [1, 2, 3, 4]. It is known that the extend of this roughening can be tuned by additives, change of the electrolyte pH, or operation within different potential windows [5, 6, 7]. In this work, we study the degradation of different platinum stepped surfaces under potential cycling to oxidative potentials. Interestingly, we quantify significantly less degradation on surfaces with narrower terraces: Ra(Pt(111)) > Ra(Pt(15 15 14)) > Ra(Pt(554)) > Ra(Pt(553)) > Ra(Pt(533)). We present here a model that explains this trend, in which steps act like sinks for both adatoms and vacancies, slowing down the nucleation and growth of the above mentioned nanoislands. We support our results, which were derived until now solely on electrochemical measurements, with in-operando Electrochemical Scanning Tunneling Microscopy (EC-STM) images.