An Investigation of Electrodeposited Platinum Metal Monolayer Catalysts By X-Ray Photoelectron Spectroscopy and Cyclic Voltammetry

Abstract

Platinum group metals (PGM) are the catalyst of choice in a wide variety of catalytic reactions, including the oxygen reduction reaction. We present here our research on tailoring the near-surface electronic structure of core/shell catalytic systems under low-loading limits of PGM overlayers fabricated via surface-limited redox replacement. Synchrotron-based XPS allowed us to profile the transitions in the electronic structure from the surface down to the adlayer/support interface and beyond. Catalyst durability is also a significant aspect for further consideration, with catalyst instability oftentimes caused by metal dissolution or corrosion. It is has been shown that Au as a supporting metal can have a stabilizing effect on Pt even under high oxidizing conditions and thus can suppress Pt dissolution, resulting in improved durability of the Pt catalysts. This study looks at the durability of Pt monolayer catalysts by subjecting them to aggressive cyclic voltammetry cycling and by examining the activity of the surfaces towards the ORR during potential cycling in an oxygen environment. Samples with an overlayer thickness of 2 monolayers or less show a more dramatic decay in electrochemically active surface area under aggressive cycling, indicating poor durability. However, Pt surface retention is significantly improved once it is at least 3 ML, indicating increased durability due to chemical state and thickness of the surface. The cycling in oxygen-rich media show markedly enhanced currents for the ORR once a 2 monolayer Pt overlayer thickness is achieved, showing the highest activity towards the ORR relative to the amount of platinum present.