https://doi.org/10.1039/D3SE01600E

This work employs photoinduced absorption spectroscopy, transient photocurrent and transient absorption spectroscopy to investigate surface recombination in BiVO4 and TiO2 photoanodes. The kinetic competition between surface recombination and water oxidation is the key limitation in the large onset potential in BiVO4. The recombination is identified via electron trapping/detrapping in vanadium oxygen vacancies. Arrhenius analyses suggest that the bias-independent 100 meV activation energy for surface recombination (trapping) is smaller than 200 meV for detrapping to generate photocurrent. In contrast, TiO2 is modestly affected by surface recombination. The faster water oxidation kinetics in TiO2 is key to suppressing surface recombination for early onset potential. Such surface recombination in BiVO4 is attributed to the slow water oxidation resulting in surface hole accumulation, opposite to TiO2 with faster water oxidation kinetics. These results emphasize the importance of enhancing water oxidation kinetics compared to surface electric field for efficient suppression of surface recombination.