Earth-Abundant Metal Oxides for Monolithic Tandem Photoelectrochemical Water Splitting Devices: Current Trends and Perspectives

Rather than supplying electrical power from a photovoltaic cell to a separate water electrolyzer, photoelectrochemical (PEC) water-splitting studies attempt to integrate key components into a single device for solar-driven hydrogen production. Despite the compact device architecture enhancing the cost-efficiency of solar-driven hydrogen production, the realization of PEC technology remains challenging. In this review, we focus on the physical properties of earth-abundant metal oxides and the choice of device architecture as key considerations for constructing a PEC device for practical hydrogen production. We introduce previous studies on BiVO₄ to elaborate on various methods for facilitating the transport of charge carriers through metal oxides and their interface with an electrolyte. Furthermore, we discuss how the choice of PEC device structures affects the electrical and ionic charge transport and the usage of precious elements. Based on this discussion, we highlight a wireless monolithic tandem PEC device made up of earth-abundant elements and expatiate on practical aspects regarding the preparation and operation of such PEC devices.