Ultrafast electronic and vibrational spectroscopy of electrochemical transformations on a metal-oxide surface during oxygen evolution from water

The oxygen evolution reaction (OER) from water fuels the planet through photosynthesis and is a primary means for hydrogen storage in energy technologies. Yet the detection of intermediates of OER central to the catalytic mechanism has been an ongoing challenge. This review covers the relevance of ultrafast electronic and vibrational spectroscopy of the electrochemical transformations of a metal-oxide surface undergoing OER. The electron doped SrTiO3/electrolyte is the system under review because of its high photocurrent efficiency with an ultrafast light trigger and because it allowed for detection of intermediate forms across the electromagnetic spectrum. The first part covers how the efficient catalytic reaction is triggered by ultrafast light pulses, describing the Schottky diode, the depletion layer, and Helmholtz layer under operating conditions to the extent possible. The second part covers the detection of the surface bound intermediates by transient spectroscopy. These target ultrafast (ps-ns) electron transfer from (or hole-trapping to) bound surface water species that are associated with the reactive oxygen intermediates of OER (e.g. OH*, O*). Their detection via a broadband visible probe, a mid-infrared evanescent wave, and coherent acoustic waves is then described. These target, respectively, the electronic states, the vibrational levels, and the lattice strain associated with the intermediates. The review is primarily concerned with how the measurements are made and the intermediates’ experimental spectra. The theoretical descriptions are brought in as a needed to provide context to spectra that are difficult to interpret on their own. A concluding section summarizes the essential findings and methodologies.