Determining the Transformation Kinetics of Water Oxidation Intermediates on Hematite Photoanode.

The oxygen evolution reaction (OER) from water is a sequential oxidation reaction process, involved in transformation of multiple reaction intermediates. For photo(electro)catalytic OER, revealing the intermediates transformation kinetics is quite challenging due to its coupling with photogenerated charge dynamics. Herein, we specifically study the transformation kinetics of the OER intermediates in rationally thin hematite photoanodes through increasing the ratio between surface intermediates and photogenerated charges in bulk. We directly identify the formation and consumption kinetics of one-hole OER intermediate (Fe═O) in photoelectrochemical water oxidation using operando transient absorption (TA) spectroscopy. The microsecond formation kinetics of the Fe═O species are sensitively changed by the excitation mode of FeO. The subsecond consumption kinetics are closely dependent on surface Fe═O species density, demonstrating that the cooperation of Fe═O intermediates is the key to accelerating water oxidation kinetics on the FeO surface. This work provides insight into understanding and controlling water oxidation reaction kinetics on FeO surface.