Temperature dependence of photoelectrochemical water oxidation and back electron-hole recombination on hematite photoanodes Shijie Yu, Daniele Benettiand, James R. Durrant Department of Chemistry & Centre for Processable Electronics (CPE), Imperial College London, London, UK Photoelectrochemical (PEC) water splitting is one of the most promising technologies for generating hydrogen fuel. The temperature dependence studies of PEC water splitting are limited to date. The key challenge that limits the efficiency of PEC water splitting is the kinetic competition between water oxidation catalysis and back electron-hole recombination (BER) due to the difference in timescales. In this study, hematite photoanode was used to study the effect of temperature dependence. Transient photocurrent (TPC) measurements and photo-induced absorption (PIA) spectroscopy were utilised to monitor surface hole densities and the dynamics of BER as a function of temperature. The TPC measurements indicate that steady-state photocurrent density decreases with increasing temperature and faster BER at a higher temperature at lower applied potential. The opposite trend was observed at higher applied potentials. The PIA spectrum reveals that accumulated surface hole densities decrease with increasing temperature and no significant change is observed for water oxidation when varying the temperature. Therefore, the temperature dependence effect of BER predominates at the lower applied potential that increases with increasing temperature, which suggests that BER recombination is thermally activated. The temperature dependence of the BER might be related to oxygen vacancies and surface states induced by doping. Therefore, hematite samples with varying levels of Ge doping are also investigated herein. These findings are contrasted with previous studies on the temperature dependence of PEC water splitting on TiO 2 . The steady-state photocurrent densities increase with increasing temperature, while the surface hole densities decrease at a higher temperature, revealing that the BER is temperature independent. Therefore, these highlight the complexities and importance of understanding the temperature effects on PEC water splitting across various metal oxide photoanodes. References 1. F. Le Formal, K. Sivula and M. Grätzel, J. Phys. Chem. C , 2012, 116 , 26707–26720. 2. F. Le Formal, S. R. Pendlebury, M. Cornuz, S. D. Tilley, M. Grätzel and J. R. Durrant, J. Am. Chem. Soc. , 2014, 136 , 2564–2574. 3. Y. Cho, T. He, B. Moss, D. Benetti, C. Liang, L. Tian, L. J. F. Hart, A. A. Wilson, Y. Taniguchi, J. Cui, M. Yang, S. Eslava, A. Yamaguchi, M. Miyauchi and J. R. Durrant, ACS Catal. , 2024, 14 , 16543–16550. 4. F. Le Formal, E. Pastor, S. D. Tilley, C. A. Mesa, S. R. Pendlebury, M. Grätzel and J. R. Durrant, J. Am. Chem. Soc. , 2015, 137 , 6629–6637. 5. C. A. Mesa, L. Francàs, K. R. Yang, P. Garrido-Barros, E. Pastor, Y. Ma, A. Kafizas, T. E. Rosser, M. T. Mayer, E. Reisner, M. Grätzel, V. S. Batista and J. R. Durrant, Nat. Chem. , 2020, 12 , 82–89.
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