Understanding reaction processes at the semiconductor/electrolyte interface is critical to developing (photo) electrochemical energy conversion systems. For the water oxidation reaction at a photoanode in a solar water splitting cell, there are multiple reaction steps that produce surface adsorbed reaction intermediates, such as OH center dot and H2O2. Little is known about how the reaction intermediate surface concentrations evolve during the water oxidation reaction. Here we use single-molecule fluorescence microscopy to track the time-dependent surface concentration of Ti-OH center dot species on TiO2 photoanodes under chopped light illumination. We correlate the reaction intermediate surface concentration with the net rate of photoelectrochemical water oxidation (i.e., the photocurrent). The reaction intermediate dynamics follow different time scales in its temporal evolution from the photocurrent dynamics. By fitting the temporal evolutions of Ti-OH center dot species and photocurrent over a range of light on/off conditions and applied potentials, we observed that the rate constants for interfacial hole transfer and O-O bond formation depend on the applied potential under illumination. The variation in the rate constants could be attributed to the presence of surface states and/or a change in the chemical nature of Ti-OH center dot species on the photoanode surface. Our findings provide insight into water oxidation kinetics under intermittent solar irradiation conditions. The Author (C) 2019. Published by ECS.