Photo-induced water oxidation via cascade charge transfer on nanostructured BiVO4/TiO2 modified with dye and co-catalyst molecules

Abstract

A titania-coated BiVO4 photoanode surface-modified with ruthenium dye Rutbipy and molecular water oxidation co-catalyst CuTCPP is fabricated for the first time. The coating of BiVO4 with transparent TiO2 nanoparticle and the subsequent deposition of Rutbipy and CuTCPP onto the TiO2 layer improves the photocurrent at the thermodynamic water oxidation potential (0.82 V vs. NHE pH 7) under 160 mW cm−2 illumination. The controlled-potential experiments under illumination reveal that the photoelectrocatalytic water oxidation activity by the dye and co-catalyst combination increases by two-fold in comparison with the co-catalyst only. A spectral monitoring of BiVO4/TiO2-Rutbipy film following a controlled-potential experiment shows the accumulation of Ru3+ formed via hole transfer from BiVO4 to the titania-bound Rutbipy. Hole transfer from Rutbipy to CuTCPP is also evident from a controlled-potential experiment conducted in the titania-only system. This study provides experimental evidence and energetic grounds for the cascade hole transfer from BiVO4 to Rutbipy and to the eventual CuTCPP, which suppress the electron-hole recombination rate and improve the water oxidation kinetics in the photoanode system.