Thermal-Stabilized Protonated TiO₂ for Heat-Accelerated Photoelectrochemical Water Splitting

Enhancing the charge separation efficiency is a big challenge that limits the energy conversion efficiency of photoelectrochemical (PEC) water splitting. Surface states generated by protonation of TiO₂ are the efficient charge separation passageways to massively accept or transfer the photogenerated electrons. However, a challenge is to avoid the deprotonation of a protonated TiO₂ photoelectrode at the operation temperature. Here, we found that the terminal hydroxyl group (OH_T) as surface states on the TiO₂ surface generated via electrochemical protonation of TiO₂ at 90 °C [90-TiO_2--(OH)] is thermally stable. As a result, the thermally enhanced photocurrent of the 90-TiO_2--(OH) electrode reached 1.05 mA cm^-2 under 80 °C, and the stability was maintained up to 10 h with a slight photocurrent decrease of 3%. The thermally stable surface states as charge separation paths provide an effective method to couple the heat field with the PEC process via thermal-stimulating hopping of polarons.