In-operando surface-sensitive probing of electrochemical reactions on nanoparticle electrocatalysts: Spectroscopic characterization of reaction intermediates and elementary steps of oxygen reduction reaction on Pt

Abstract In this paper we present an in-operando spectroscopic study of the reaction intermediates involved in ORR on electrified Pt nanoparticle electrocatalysts. To accomplish this, we have synthesized Ag-Pt core-shell nanoparticles, that contain a thin shell of Pt (∼ 1 nm) uniformly deposited on a larger Ag core (∼ 60 nm). We show that these nanostructures are ideal platforms for in-operando Plasmon Enhanced Raman Spectroscopy (PERS) of ORR on Pt. We combined these PERS studies with DFT calculations to assign the measured vibrational spectra to relevant surface intermediates as a function of electrocatalyst potential. These vibrational assignments were further verified and validated by performing PERS measurements using de-oxygenated and heavy oxygen (O2-18) saturated electrolyte. These studies allowed us to identity the presence of critical reaction intermediates (OH, O2, OOH, and H2O) as the function of operating voltage on the Pt surface and derive voltage-dependent elementary step mechanisms of the reaction.