Solar-Driven Z-scheme Water Splitting Using Modified BaZrO3-BaTaO2N Solid Solutions as Photocatalysts

A two-step photocatalytic water splitting (Z-scheme) system consisting of a modified BaZrO3–BaTaO2N solid solution, a paired photocatalyst, and a reversible donor/acceptor pair (i.e., redox mediator) was constructed. BaZrO3–BaTaO2N (Zr/Ta = 0.05) having a band gap of 1.8 eV has sufficient potential to reduce and oxidize water by absorbing visible photons of up to 660 nm. Upon suitable modification of this material with nanoparticulate cocatalysts, both H2 and O2 were evolved individually in the presence of reversible redox couples (viz., IO3–/I– and Fe3+/Fe2+), although O2 evolution from aqueous solution containing Fe3+ was negligible. Among various combinations tested, BaZrO3–BaTaO2N modified with Pt nanoparticles was the most suitable for H2 evolution in the presence of an IO3–/I– pair, achieving Z-scheme water splitting into H2 and O2 in combination with either PtOx/WO3 or TiO2 rutile as an O2 evolution photocatalyst even under simulated sunlight.