Dynamic charge collecting mechanisms of cobalt phosphate on hematite photoanodes studied by photoinduced absorption spectroscopy

Reaction sites, surface states, and surface loaded electrocatalysts are photoinduced charge storage sites and critical to photoelectrochemical (PEC) performance, however the charge transfer mechanisms involved in the three remain poorly understood. Herein, we studied the charge transfer processes in hematite (Fe₂O₃) without/with loaded cobalt phosphate (CoPi) by operando photoinduced absorption (PIA) spectroscopy. The loaded CoPi receives trapped holes in surface states at low potential and directly captures holes in the valence band at high potential. Through the dynamic hole storage mechanisms, loaded CoPi on Fe₂O₃ facilitates spatial charge separation and serves as a charge transfer mediator, instead of serving as a catalyst to change the water oxidation mechanism (constant third-order reaction). The spatial separation of photoinduced charges between Fe₂O₃ and CoPi results in more long-lived holes on the Fe₂O₃ surface to improve PEC water oxidation kinetically. The dynamic charge collecting mechanism sheds light on the understanding and designing of electrocatalyst loaded photoanodes.

Loaded CoPi on Fe₂O₃ facilitates spatial charge separation by dynamic hole storage mechanisms, in which CoPi receives trapped holes in surface states at low potential and directly captures holes in the valence band at high potential.