Recent Developments in Visible-Light-Absorbing Semitransparent Photoanodes for Tandem Cells Driving Solar Water Splitting

Abstract

The development of an efficient conversion system to transform solar energy into chemical energy, such as renewable hydrogen, is a promising way to overcome energy problems. Photoelectrochemical (PEC) water splitting is a promising means of obtaining renewable hydrogen directly from water utilizing sunlight. Recent reports have demonstrated that a PEC cell with a tandem configuration (tandem cell) has the potential to realize a high solar-to-hydrogen (STH) energy conversion efficiency by solar water splitting. However, there are still many obstacles to the development of practical and cost-effective tandem cells. In particular, development of efficient photoanodes for the oxygen evolution reaction (OER) is a prerequisite for improving the STH efficiency. Herein, recent progress in developing (semi)transparent photoanodes for the OER, such as Fe2O3, BiVO4, and Ta3N5, is described based on the topics of preparation methods, semiconductor properties, and PEC performance. In addition, the strategies for enhancing the STH efficiency of tandem cells consisting of (semi)transparent photoanodes conjugated with photovoltaic (PV)-based cathodes are summarized. This Review is expected to provide guidelines for the future development of tandem cells capable of highly efficient and stable water splitting.