Work-Function-Resolved Imaging of Relaxation Oscillations and Chemical Spillover in CO Oxidation over Platinum Surfaces

TL;DR

This study employs combined operando microscopy techniques to achieve work-function-resolved imaging of CO oxidation reaction fronts on platinum, revealing detailed insights into chemical spillover and oscillation mechanisms.

Contribution

First work-function-resolved imaging of reaction fronts during CO oxidation on platinum surfaces using FM-KPFM combined with electron microscopy.

Findings

Identified rapid oxygen coverage onset and gradual relaxation back to CO coverage.

Reproduced wave morphology with reaction-diffusion simulations.

Demonstrated heterogeneity and asymmetry in chemical spillover processes.

Abstract

Chemical waves of CO oxidation on platinum surfaces exhibit complex spatio-temporal self-oscillations, yet the local electronic mechanisms driving their propagation remain poorly understood under operando conditions. In this work, we combine operando scanning electron microscopy with frequency-modulated Kelvin probe force microscopy (FM-KPFM) to simultaneously map secondary electron contrast and local work-function variations during CO oxidation on Pt. By utilizing the KPFM tip as a localized sensor, we provide the first work-function-resolved imaging of reaction fronts, enabling an unambiguous physical assignment of CO- and oxygen-covered states. Our results demonstrate that the spillover process of chemical wave-the transition and expansion of adsorbate phases-is characterized by a pronounced temporal asymmetry and spatial heterogeneity transition thresholds. KPFM identifies a rapid onset of oxygen coverage followed by a gradual, diffuse relaxation back to the CO-covered state, indicative of relaxation-type oscillations even at low pressures (10^-2 Pa). Correlative reaction-diffusion simulations reproduce this wave morphology, confirming that the high-resolution work-function signal provides unique insights into the internal structure and kinetic heterogeneity of the working catalyst surface.