Photoelectrochemical and Catalytic Hydrogen Generation from Hydrolysis of NaBH₄ using Ruthenium and Platinum Decorated ZnO/TiO₂ Heterojunction Thin Film Electrodes

In this study, the use of ruthenium (Ru) and platinum (Pt)-decorated zinc oxide-titanium oxide (ZnO/TiO2) nanostructured catalysts for catalytic and photoelectrochemical (PEC) sodium borohydride (NaBH4) hydrolysis for hydrogen production was investigated. Catalytic studies of ZnO/TiO2/Ru-Pt electrodes conducted under dark conditions have shown that the hydrolysis process does not depend on the structure of the catalyst. In contrast to the dark catalytic measurements, it was found that the morphology of the nanocatalyst and the metal used to sensitize the nanocatalyst affected the PEC performance. From the BET analysis, ZnO nano-flower (NF) structures have a surface area of 80 m(2)g(-1), while the surface area of nanosheet (NS) structures is calculated as 17 m(2)g(-1). In parallel with their high surface area, ZnO NF structures were found to have higher optical absorption in the UV and visible region than NS structures. However, the high photosensitivity of NS structures compared to the NF enabled them to exhibit very good PEC performance, especially at high NaBH4 concentrations. In this study, the highest applied bias photoconversion efficiency was observed in ZnO NS/TiO2/Ru catalysts with 9.0%. This very high efficiency indicates the enormous potential of this catalyst for next-generation green hydrogen production.