View article

It has been more than 40 years since Fujishima and Honda demonstrated water splitting using TiO₂, yet there is still no clear mechanism by which surface holes on TiO₂ oxidize water. In this paper, we use a range of complementary techniques to study this reaction that provide a unique insight into the reaction mechanism. Using transient photocurrent and transient absorption spectroscopy, we measure both the kinetics of electron extraction (t_50% ≈ 200 μs, 1.5V_RHE) and the kinetics of hole oxidation of water (t_50% ≈ 100 ms, 1.5V_RHE) as a function of applied potential, demonstrating the water oxidation by TiO₂ holes is the kinetic bottleneck in this water-splitting system. Photoinduced absorption spectroscopy measurements under 5 s LED irradiation are used to monitor the accumulation of surface TiO₂ holes under conditions of photoelectrochemical water oxidation. Under these conditions, we find that the …