Thermal-Stabilized Protonated TiO 2 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 TiO ₂ 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 TiO ₂ photoelectrode at the operation temperature. Here, we found that the terminal hydroxyl group (OH _T ) as surface states on the TiO ₂ surface generated via electrochemical protonation of TiO ₂ at 90 °C [90-TiO _{2- x} -(OH) _x ] is thermally stable. As a result, the thermally enhanced photocurrent of the 90-TiO _{2- x} -(OH) _x 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.