Operando x-ray absorption spectroscopy unveils light-driven redox dynamics at the semiconductor/cocatalyst interface.

Area of Science:

• Materials Science
• Electrochemistry
• Photocatalysis

Background:

• Cobalt-based mixed oxides are key oxygen evolution reaction (OER) catalysts.
• Their function as photoelectrochemical cocatalysts under irradiation is not well understood.
• Operando studies are needed to probe irradiation-induced structural changes.

Purpose of the Study:

• To investigate the redox dynamics of cobalt-iron oxide (CoFeOₓ) cocatalysts in semiconductor photoanodes.
• To understand the role of interfacial structure and light in modulating catalytic activity for solar water splitting.
• To elucidate charge transfer mechanisms at the semiconductor/cocatalyst interface.

Main Methods:

• Utilized operando X-ray absorption spectroscopy (XAS) combined with fixed-energy X-ray absorption voltammetry (FEXRAV).
• Probed cobalt oxidation states at the semiconductor/cocatalyst interface under both dark and illuminated conditions.
• Analyzed element-selective changes to understand interfacial charge transfer.

Main Results:

• Discovered a novel interfacial cobalt state influencing catalytic activity.
• Observed light-induced reduction in cobalt oxidation state and a cathodic shift in redox potentials.
• Identified a photocatalytic cycle distinct from the dark-state electrocatalysis, showing light's impact on rate-determining steps.

Conclusions:

• Interface structure plays a critical role in tuning the catalytic activity of CoFeOₓ cocatalysts.
• Light significantly modulates the catalytic behavior and redox potentials of the cocatalyst.
• Operando X-ray techniques are powerful tools for understanding interfacial charge transfer and designing efficient photoelectrochemical systems for solar water splitting.