Work-Function-Resolved Imaging of Relaxation Oscillations and Local Kinetic Heterogeneities in CO Oxidation over Platinum Surfaces

High Resolution Image Download MS PowerPoint Slide Chemical waves of CO oxidation on platinum surfaces exhibit complex spatiotemporal 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 transition and expansion of adsorbate phases are characterized by a pronounced temporal asymmetry and spatial heterogeneity. 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.