Measuring Charge Selective Contacts on Semiconducting Photocatalyst Particles

Water splitting could replace steam-methane reforming, a carbon intensive process, to generate hydrogen for energy storage, fertilizer production, and many other industrial processes. Photoelectrochemical (PEC) overall water splitting (OWS), for example, produces hydrogen from water, without wires or applied voltages, via a clean and renewable energy source, sunlight. To do so, PEC particles or photocatalysts (PC) must absorb light, and selectively collect the generated carriers, either electrons or holes, at specific sites which drive reduction or oxidation reactions, respectively. While theoretical solar to hydrogen (STH) efficiencies are at least 18%, state-of-the-art PCs are below 3%. Despite the extreme efforts screening and tuning semiconductor photocatalysts, a thorough understanding and control of electronic properties of the semiconductor-electrocatalysts (sem|cat) interface is limited. Here, we use advanced electrochemical methods (dual-working electrode), scanning probe microscopy (conductive-AFM) and ambient-pressure XPS to measure and understand the origins of the electrochemical driving force (gradient in electrochemical potential) developed at complimentary electrocatalysts on photocatalyst particles. We use the dual-working electrode geometry on a high-quantum-yield wide-bandgap perovskite oxide, SrTiO3, to demonstrate the adaptive nature of electrocatalysts, Pt and CoOx, as they accumulate electrons and holes respectively. The cooperativity of half-reaction kinetics and adaptive sem|cat barrier height will be demonstrated along with the influence of crystal termination, which we argue is commonly overemphasized. Finally, a new contactless method of measuring the photovoltage at chemically distinct catalysts sites will be presented. Measured photovoltage induced shifts to element specific core levels in ambient pressure XP spectra in the dark and under illumination directly probe interfacial mechanisms operando. In sum, the introduced techniques and their findings demonstrate the underlying mechanisms and the degree that they play, enabling directed research of photocatalyst systems under one dominant engineering condition, charge selective Figure 1