Comparison of homogeneous and heterogeneous catalysts in dye-sensitised photoelectrochemical cells for alcohol oxidation coupled to dihydrogen formation.

This study examines two strategies-homo- and heterogeneous approaches for the light-driven oxidation of benzyl alcohol in dye-sensitised photoelectrochemical cells (DSPECs). The DSPEC consists of a mesoporous anatase TiO film on FTO (fluorine-doped tin oxide), sensitised with the thienopyrroledione-based dye as the photoanode and an FTO-Pt cathode combined with a redox-mediating catalyst. The homogeneous catalyst approach entails the addition of the soluble 2,2,6,6-tetramethylpiperidine-1-oxyl () to the DSPEC anolyte, while the heterogeneous strategy employs immobilisation of a analogue with a silatrane anchor () onto the photoanode. Irradiation of the photoanode oxidises the -moiety to , both in the homogeneous and the heterogeneous system, which is a chemical oxidant for benzyl alcohol oxidation. Photoanodes containing the heterogeneous demonstrate decreased photocurrent, attributed to introducing alternative pathways for electron recombination. Moreover, the immobilised demonstrates an insufficient ability to mediate electron transfer from the organic substrate to the photooxidised dye, resulting in device instability. In contrast, the homogeneous approach with as a redox-mediating catalyst in the anolyte is efficient in the light-driven oxidation of benzyl alcohol to benzaldehyde over 32 hours, promoted by the efficient electron mediation of between and the organic substrate. Our work demonstrates that operational limitations in DSPECs can be solved by rational device design using diffusion-mediated electron transfer steps.