Estimations of the Activation Energies for the Charge Transfers of the Long-Lived Holes at the Semiconductor/Electrolyte Interfaces of α-Fe2O3 and α-Fe2O3/Co–Pi Photoanodes

Cobalt phosphate (Co–Pi) is an efficient co-catalyst known to enhance charge transfer efficiency and lower activation energy, improving photoelectrochemical (PEC) performance. In this study, we estimated the activation energy for hole transfer at the interface between hematite (α-Fe₂O₃) and Co–Pi. By using a near-field heterodyne transient grating (NF-HD-TG) method, we determined the reaction rate constants for the hole transfer under an applied bias voltage. The activation energy and the pre-exponential factor (A) could be extracted from the temperature-dependent rate constants. After the surface treatment with Co–Pi, the activation energy was significantly reduced from 103.8 to 27.5 kJ/mol. Furthermore, the pre-exponential factor also decreased, indicating that the limited Co–Pi deposition may have reduced the overall active surface area for the water oxidation reaction.