Photoelectrochemical Performance for Water Oxidation Improved by Molecular Nickel Porphyrin-Integrated WO3/TiO2 Photoanode

A WO3/TiO2 heterojunction photoanode was prepared by insitu growth of WO3 on a mesoporous TiO2 electrode. The photoinduced charge-transfer properties and chargeseparation improvement in this kind of type-II heterojunction were characterized by transient surface photovoltage spectra. By using sulfite oxidation as a hole scavenger, we demonstrated that 72% of the photo-generated holes are reaching the surface of the photoanode, but the efficiency of hole injection (eta(ox)) into the electrolyte was only 48%. For the first time, a Ni(II)meso-tetra(4-carboxyphenyl)porphyrin (NiTCPP) was incorporated as a water oxidation catalyst into the WO3/TiO2 heterojunction photoanode, which promoted the value of eta(ox) to 81%. The maximum applied bias photon-to-current efficiency for the WO3/TiO2/NiTCPP photoanode was determined to be 0.2% at 1.01V vs. the reversible hydrogen electrode (RHE), under which condition a Faradic efficiency of 89% for water oxidation was achieved (averaged over 1h of photolysis).