Speaker: Scott A. Chambers, Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory Richland, Washington, U.S.A.
Harvesting sunlight to drive the water splitting reaction via electrochemical means represents a grand challenge in energy science. This reaction is difficult for both thermodynamic and kinetic reasons. Not only must photogenerated electrons and holes be sufficiently energetic to drive the two half-cell reactions, but these carriers must also cross their respective solid/liquid interfaces in a facile way. Additionally, the photoelectrode surfaces must be stable against photocorrosion. Finally, electron and hole mobilities must be high in order that transport through the electrode material not be the rate-limiting step. These stringent requirements bring significant challenges to the materials science of water photoelectrolysis. We have used epitaxial complex oxides, prepared by molecular beam epitaxy, to fabricate model pn junctions in order to explore these phenomena at a fundamental level. Specifically, we have synthesized SrxLa1-xCrO3, SrZrxTi1-xO3 and LaFeO3 and have investigated the associated structural, electronic, optical, photophysical and photochemical properties of heterojunctions formed when these films are deposited on n-SrTiO3(001) and p-Ge(001). We have also explored the properties of Fe2CrO4 grown on MgO(001). These experiments, and related first-principles modelling, are aimed at gaining fundamental understanding of the various processes involved in water splitting. In this talk, I will give highlights of these investigations and offer a perspective on the fundamental science challenges that need to be addressed in order to rationally design workable photoelectrochemical electrodes.