Dye-Sensitized Hydrobromic Acid Splitting for Hydrogen Solar Fuel Production

Hydrobromic acid (HBr) has significant potential as an inexpensive feedstock for hydrogen gas (H₂) solar fuel production through HBr splitting. Mesoporous thin films of anatase TiO₂ or SnO₂/TiO₂ core-shell nanoparticles were sensitized to visible light with a new Ru^II polypyridyl complex that served as a photocatalyst for bromide oxidation. These thin films were tested as photoelectrodes in dye-sensitized photoelectrosynthesis cells. In 1 N HBr (aq), the photocatalyst undergoes excited-state electron injection and light-driven Br^- oxidation. The injected electrons induce proton reduction at a Pt electrode. Under 100 mW cm^-2 white-light illumination, sustained photocurrents of 1.5 mA cm^-2 were measured under an applied bias. Faradaic efficiencies of 71 ± 5% for Br^- oxidation and 94 ± 2% for H₂ production were measured. A 12 μmol h^-1 sustained rate of H₂ production was maintained during illumination. The results demonstrate a molecular approach to HBr splitting with a visible light absorbing complex capable of aqueous Br^- oxidation and excited-state electron injection.