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 RuII 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.