Resonant Photoelectron Spectroscopy from Liquids and Solid-liquid Interfaces

Significant effort is being invested to find abundant, catalytically active and stable (photo)electrocatalysts, with transition metal oxides being an associated promising material class. The issues of efficiency and stability are due to related electronic-structure processes driving the oxygen evolution reaction and hydrogen evolution reaction at the solid-liquid interface between the electrocatalyst and the electrolyte. I will present our spectroscopic results on several transition metal oxide nanoparticles dissolved in water, which mimicked the interface of relevant (photo)electrocatalysts for water splitting in their true environment by using soft-X-ray synchrotron photoemission spectroscopy in combination with the liquid microjet technique. Most pressing questions regarding the molecular-level understanding of such buried interfaces are how ions adsorb at the solid–solution interface, how interfacial ions are solvated, how the solvent molecules respond, and how all this affects charge-state and energy transfer across the interface.

I will then give a short overview of our (valence) ambient-pressure photoelectron and Auger- electron spectroscopy studies on solid (photo)electrocatalysts (either as thin film or as supported nanoparticles), on which a thin film of liquid water has been deposited. The important questions that we wanted to answer are whether the catalytic processes affect only the chemical nature of the electrode surface, or do they also induce chemical (phase) changes in the bulk material. What is the molecular and electronic structure of the catalyst when a voltage is applied? How is the molecular-orbital interplay between the oxygen and the transition metal in the catalyst? And what is the effect of electrolyte on the electronic structure during the oxygen evolution reaction?