Mixed Transition Metal Oxides for Photoelectrochemical Hydrogen Production

Abstract

Photoelectrochemical (PEC) water splitting is a process of separating water into clean hydrogen and oxygen gases using photocatalysts. The major challenge in PEC water splitting is the development of photocatalysts with appropriate properties for efficient and cost-effective practical production of hydrogen. The use of nanocrystalline metal oxides as photocatalysts is one of the promising routes of producing hydrogen fuel efficiently and cheaply. However, the transition metal oxides (TMOs) used today still have tremendous limitations of high cost, low visible light harvesting capacities, inefficient charge separation and transportation, and poor stability in water. The solution to these limitations is being sought by energy materials researchers by exploiting a variety of uncommon properties of TMOs through synthesis and combination of TMOs to form various mixed transition metal oxides (MTMOs) thin films and MTMOs architectures. Thus, this work focused on the review of various TMOs and MTMOs and the strategies attempted to improve the efficiency of two basic reactions of evolution hydrogen and oxygen evolution in PEC water splitting. The major outcomes of this survey are: (a) major research efforts in this direction focused on adjusting the chemical composition and modifying morphologies of the materials using nanotechnology processing routes that led to the creation of thin thicknesses, high surface areas and active sites, and enhanced electrocatalytic activities of the metal oxides; (b) despite advances in finding a cheaper and more efficient alternative to Pt cathode, the electrocatalytic activity of TMOs is still much lower to the state-of-the-art Pt cathode, and therefore simple and effective strategies are still required to develop effective metal oxide-based photocathode for hydrogen production.