Hydrogen production from formic acid solution by modified TiO₂ and titanate nanotubes in a two-step system under visible light irradiation

Hydrogen gas is one of the most promising renewable energy sources, and the final product of hydrogen combustion is nothing but water. However, it is still a big challenge to produce hydrogen and store it. Many studies have been conducted into produce hydrogen from water using photocatalysts. Z-scheme photocatalysis is a two-photocatalyst system that comprises a hydrogen catalyst and an oxygen catalyst to produce hydrogen and oxygen respectively. Compared to the one-step system, the two-step system can promote the efficiency of water splitting. In addition, formic acid (FA) is a convenient hydrogen-storage material and can be safely handled in aqueous solutions. Therefore, this study investigated the photocatalytic conversion of FA solution to hydrogen using visible light with several types of hydrogen catalysts (CdS/titanate nanotubes (TNTs), CdS/TiO₂, Pt/CdS/TNTs) and WO₃ as the oxygen catalyst. The results showed that the yield of hydrogen with CdS/TNTs + WO₃ was much higher than with CdS/TiO₂ + WO₃. Moreover, coating the photocatalysts with metal could further promote the reaction. The optimal platinum loading was 0.01 wt%, and the hydrogen production achieved was 852.5 μmol · h⁻¹ with 20 vol% FA solution.