Electron transfer across solid/liquid interfaces: elucidating elementary processes from femtoseconds to seconds
Building fuel cells, electrolyzers or photoelectrochemical cells based on water (photo)electrolysis is extremely challenging. One origin of this challenge is the complexity of the underlying physical chemistry. Most such devices require transfer of electrons between solid(s) and water and thus building the best possible devices requires understanding the link between transient changes in bulk solid electronic structure, interfacial electronic structure and interfacial chemistry. Essentially all existing approaches address only part of this picture: e.g. they only probe electronic structure (optical absorption), or extracted current or provide elemental insight but are insensitive to the presence of hydrogen (x-ray absorption). 

In SOLWET, I will address this gap using interface-specific optical spectroscopies, in the visible and infrared, to probe interfacial electronic and vibrational transitions and their coupling. By combining these probes with an additional intense laser pulse I will watch (photo)electrolysis of water in real time as it happens. In particular, I will directly probe the coupling of transiently perturbed solid electronic structure to interfacial electronic structure and watch how this perturbation drives water’s oxidation, for a hematite photoanode, or reduction, for a Pt cathode, through the interfacial vibrational response. By describing how these couplings change with solid modification (e.g. an alumina overlayer on hematite) or changes in aqueous solution composition (e.g. changing the pH in contact with Pt) the results of SOLWET will offer the physical insights necessary to build the best possible hematite and Pt containing photoelectrochemical devices. Moreover, because the novel all-optical tools developed in SOLWET are not system-specific, the approach demonstrated in this work will be widely applicable.