Solar light driven atomic and electronic transformations in a plasmonic Ni@NiO/NiCO photocatalyst revealed by ambient pressure X-ray photoelectron spectroscopy.

This work employs ambient pressure X-ray photoelectron spectroscopy (APXPS) to delve into the atomic and electronic transformations of a core-shell Ni@NiO/NiCO photocatalyst - a model system for visible light active plasmonic photocatalysts used in water splitting for hydrogen production. This catalyst exhibits reversible structural and electronic changes in response to water vapor and solar simulator light. In this study, APXPS spectra were obtained under a 1 millibar water vapor pressure, employing a solar simulator with an AM 1.5 filter to measure spectral data under visible light illumination. The APXPS spectra indicate that the metallic Ni core absorbs the light, exciting plasmons, and creates hot electrons that are subsequently utilized through hot electron injection in the hydrogen evolution reaction (HER) by NiCO. Additionally, the data show that NiO undergoes reversible oxidation to NiOOH in the presence of water vapor and light. The present work also investigates the contribution of carbonate and its involvement in the photocatalytic reaction mechanism, shedding light on this seldom-explored aspect of photocatalysis. The APXPS results highlight the photochemical reduction of carbonates into -COOH, contributing to the deactivation of the photocatalyst. This work demonstrates the APXPS efficacy in examining photochemical reactions, charge transfer dynamics and intermediates in potential photocatalysts under near realistic conditions.