Cyclic Voltammetry–Synchronized Operando HERFD-XANES and RIXS Analyses of Adsorbed Structures and Bonding States of Active Oxygen Species on Pt Nanoparticle Electrocatalysts in PEFC

This study presents an operando analysis of Pt nanoparticle (NP) electrocatalysts in a polymer electrolyte fuel cell (PEFC) under cyclic voltammetry (CV), utilizing a multimodal system combining high-energy resolution fluorescence detected X-ray absorption near-edge structure (HERFD-XANES), resonant inelastic X-ray scattering (RIXS), X-ray diffraction (XRD), and quick X-ray absorption fine structure (QXAFS) techniques. The developed multi-analysis provides insight into the voltage-dependent adsorption structures and bonding states of active oxygen species on Pt NPs. CV-synchronized HERFD-XANES spectra reveal the evolution of Pt electronic states, highlighting shifts in bonding characteristics associated with changes in the applied voltage. In the anodic scan, oxygen species adsorb on Pt NPs at specific voltages, inducing structural changes that can be detected via XRD and QXAFS analysis. Density functional theory (DFT) calculations combined with finite difference method near-edge structure (FDMNES) simulations predict the stability and binding configurations of adsorbed oxygen species, emphasizing the role of edge sites of Pt NPs in the oxygen reduction reaction (ORR) activity. Additionally, the study evaluates degradation effects through accelerated durability tests (ADT), showing how Pt NP coarsening impacts adsorption dynamics and the electronic structure under ADT cycling. The CV processes were visualized by operando HERFD-XANES and RIXS spectroscopies. The findings demonstrate the potential of CV-synchronized HERFD-XANES and RIXS to provide atomistic insights into catalytic mechanisms on Pt NPs, supporting the optimization of Pt-based electrocatalysts for improved performance and durability in PEFC applications.