Water Splitting Using High Temperature Solid Oxide Photoelectrochemical Cell and Visible Sunlight: Searching for the Appropriate Semiconductor Materials

In this paper, the concept of using solid oxide photoelectrochemical cells (SOPCs) to split water at high temperature using visible sunlight was experimentally investigated, in order to search for the appropriate semiconductor materials. High temperature photoelectrochemical water splitting physically broadens the selection of potential applicable semiconductor materials and enables more visible sunlight absorption. This newly conceived concept provides a unique pathway for solar hydrogen production, compared to conventional photoelectrochemical cells (PECs) that require aqueous environments, though experimental validation is needed. The main focus of this study was on the fabrication and evaluation of high temperature diodes suitable for use as the photocatalytic/oxygen electrodes of SOPCs. The rectifying characteristics of TiO2 based diodes, including Ag/TiO2, LSM/TiO2, LSC/TiO2, and LSCF/TiO2, were investigated at elevated temperatures. Among those diodes, only LSM/TiO2 demonstrated acceptable rectifying properties up to 450 degrees C, indicating that such configuration may be applicable to the proposed SOPC. The results also excluded Schottky diodes from the candidates due to their rapidly degrading rectifying behaviors at elevated temperatures. Candidate semiconductors for the photovoltaic (PV) part of the cell and electrolytes for the electrolysis part were also identified and summarized in this paper for future investigations. (C) 2017 The Electrochemical Society. All rights reserved.