Tantalum (oxy)nitride based photoanodes for solar-driven water oxidation

Photoelectrochemical (PEC) water splitting is a very promising process to produce hydrogen as a clean energy carrier. To achieve 10% solar to hydrogen (STH) conversion efficiency required for practical applications, the current central task in PEC water splitting is the development of efficient photoelectrodes, particularly photoanodes for water oxidation, used in PEC cells. Tantalum (oxy)nitrides with bandgaps ranging from 2.5 to 1.9 eV, corresponding to theoretical STH efficiencies varying from 9.3% to 20.9%, are considered a class of attractive light adsorbers for use in photoanodes for PEC water oxidation and have attracted much recent research attention. In this review, the recent development of tantalum (oxy) nitride photoanodes is summarized. Special interest is focused on the synthesis methods of tantalum (oxy) nitride films and important approaches for improving PEC conversion efficiency and stability of these films as photoanodes. The future trends of tantalum (oxy) nitride based photoanodes are also discussed.