Oxidation of water provides the electrons and protons needed for the generation of fuels in any solar fuel system. In order to guide catalyst performance improvement, knowledge of the detailed mechanism of the four-electron oxidation of water to oxygen at the elementary step level is required. This has proved especially challenging for robust, Earth abundant metal oxide catalysts. Electrokinetic methods and ex situ or in situ steady state spectroscopy have revealed some insights into rate limiting steps or structural phase transformations of the catalyst under applied potential. Recent observation of surface reaction intermediates with rapid-scan FT-IR spectroscopy under reaction conditions with temporal resolution of milliseconds has allowed to establish the molecular structure and kinetic relevancy of transient species, and to identify their role in the catalytic cycle.