It is particularly challenging to achieve the high efficiency needed for the overall reaction to be energetically sustainable due to its multi-step nature. Some researchers believe that the inefficient utilization of photogenerated holes in photocatalytic and photoelectrochemical water oxidation processes is the root cause of poor efficiency. Several critical factors have been identified. First, high recombination rates between holes and electrons remove a considerable fraction of photogenerated holes before they can participate in oxidation reactions. Second, surface defects and impurities trap photogenerated holes and prevent them from reaching the reaction sites. Third, intrinsic material limitations such as low light absorption and poor charge mobility hinder the effective generation, transport and utilization of holes. Last, photodegradation of the photoabsorber caused by unutilized holes, reduces its stability and effectiveness in water splitting. There is another factor that can control rates which has not been strongly considered so far for photo-OER: not all reaction steps in the catalytic mechanism involve hole dynamics, depending instead on thermal energy. Key thermal steps include unimolecular decomposition of surface intermediates to release H + and O2, and bimolecular coupling steps to form the final O-O bond. Those thermal steps can dominate the overall rate of a photo-driven reaction, which has recently been identified in a kinetics modeling study of photo-OER using a molecular dyecatalyst diad. These considerations raise the question: do thermal steps only affect photo-OER in molecular systems or are they also important on the surfaces of inorganic photocatalytic and photoelectrocatalytic materials? Photo-OER on TiO2 is a useful model system to address this question because of the extensive literature on both the rutile and anatase phases and numerous proposals for favored reaction pathways based on diverse, detailed experiments and theory. This literature enables construction of a physically-based and chemically detailed stochastic reaction-diffusion kinetics computational model that can provide insights to factors controlling photo-OER.