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

Area of Science:

• Surface science
• Heterogeneous catalysis
• Chemical kinetics

Background:

• Chemical waves of CO oxidation on platinum surfaces display complex self-oscillations.
• The local electronic mechanisms governing wave propagation under reaction conditions are not well understood.

Purpose of the Study:

• To investigate the local electronic mechanisms driving chemical wave propagation during CO oxidation on platinum surfaces under operando conditions.
• To provide work-function-resolved imaging of reaction fronts for unambiguous assignment of adsorbate states.

Main Methods:

• Operando scanning electron microscopy (SEM) combined with frequency-modulated Kelvin probe force microscopy (FM-KPFM).
• Simultaneous mapping of secondary electron contrast and local work-function variations.
• Localized sensing using the KPFM tip.

Main Results:

• First work-function-resolved imaging of reaction fronts during CO oxidation on Pt.
• Demonstration of pronounced temporal asymmetry and spatial heterogeneity in adsorbate phase transitions.
• Identification of rapid oxygen coverage onset followed by gradual CO-covered state relaxation, indicative of relaxation-type oscillations even at low pressures (10⁻² Pa).

Conclusions:

• High-resolution work-function imaging provides unique insights into the internal structure and kinetic heterogeneity of working catalyst surfaces.
• Correlative reaction-diffusion simulations support the observed wave morphology and kinetic heterogeneity.
• The findings elucidate the electronic mechanisms behind spatiotemporal self-oscillations in catalytic reactions.