Light-driven water oxidation by a BiVO4/TiO2 photoanode modified with D102 organic dye and copper(<sc>ii</sc>) meso-tetra(4-carboxyphenyl)porphyrin

To improve its photoelectrocatalytic water oxidation properties, the BiVO4 photoanode was integrated with TiO2 modified by Indoline D102 dye and copper(ii) meso-tetra(4-carboxyphenyl)porphyrin (CuTCPP). The dye was used as a redox mediator, whereas CuTCPP served as a co-catalyst for light-driven water oxidation. The systematic modifications on photoanodes were meticulously characterized by SEM, XRD, UV-Vis spectrometry, and potentiostatic analyses. Modification of the BiVO4 photoanode with TiO2 followed by D102 and CuTCPP (BiVO4/TiO2/D102-CuTCPP) demonstrates a remarkable improvement in photoelectrocatalytic water oxidation properties compared to those of the unmodified BiVO4 film. An increase of power density up to 20 fold was observed under 100 mW cm-2 light irradiation at a bias potential of 1.27 VRHE. The system also demonstrated good stability, with a photocurrent retention of around 97% of the initial photocurrent over a 20 minutes period and retaining 69% of its initial value after 2 hours of continuous operation. Furthermore, the photoelectrocatalytic water splitting exhibited a high faradaic efficiency of oxygen evolution at approximately 97%. These excellent performances were attributed to the synergy of dye and co-catalyst co-assembly by forming a cascade hole transfer mechanism which improves the water oxidation kinetics and reduces the electron-hole recombination rate of BiVO4 in the photoanode system.