Electric-field-promoted photo-electrochemical production of hydrogen from water splitting

Abstract

Given that conversion efficiencies of incident solar radiation to liquid fuels, e.g., H2, are of the order of a few percent or less, as quantified by ‘solar to hydrogen’ (STH), economically inexpensive and operationally straightforward ways to boost photo-electrochemcial (PEC) H2 production from solar-driven water splitting are important. In this work, externally-applied static electric fields have led to enhanced H2 production in an energy-efficient manner, with up to ~30–40% increase in H2 (bearing in mind field-input energy) in a prototype, open-type solar cell featuring rutile/titania and hematite/iron-oxide (Fe2O3), respectively, in contact with an alkaline aqueous medium (corresponding to respective relative increases of STH by ~12 and 16%). We have also performed non-equilibrium ab-initio molecular dynamics in both static electric and electromagnetic (e/m) fields, for water in contact with a hematite/iron-oxide (001) surface, observing enhanced break-up of water molecules, by up to ~70% in the linear-response régime. We discuss the microscopic origin of such enhanced water-splitting, based on experimental and simulation-based insights. In particular, we external-field direction at the hematite surfaces, and scrutinise properties of the adsorbed water molecules and OH– and H3O+ species, e.g., hydrogen bonds between water-protons and the hematite surfaces’ bridging oxygen atoms, as well as interactions between oxygen atoms in adsorbed water molecules and underlying iron atoms.