Understanding Photovoltage in Insulator-Protected Water Oxidation Half-Cells

In the pursuit of a photosynthetic and efficient water splitting device, detailed investigations of individual aspects of the whole device are necessary: catalysis, electronic conductivity, cathode and anode stability, and kinetics among other aspects. Improvement in one aspect can, however, often require fundamental tradeoffs affecting others. High solar-to-hydrogen efficiency of the overall system is the ultimate goal of water splitting research. When optimizing half-cells, either the anode or cathode, the photovoltage required to achieve a current density of interest is an especially important metric. This report investigates the photovoltage in insulator-protected water oxidation anodes using ALD-TiO2 protected silicon devices as a case study and looks in depth at how photovoltage is correctly determined from typical electrochemical analysis and how this relates to the underlying solid-state carrier transport. Finally, the photovoltage at 10 mA/cm(2) referenced to the thermodynamic potentials is reviewed from several leading research reports for various photoanodes and photocathodes, providing a direct comparison of cell performance. (C) The Author(s) 2015. Published by ECS. All rights reserved.