The (mu)-oxo-bridged complex, [((OH)(2)OP-tpy)(H2O)(2)RuORu(OH2)(2)(tpy-PO(OH)(2))](4+) (tpy-PO(OH)(2) is 4'-phosphonato-2,2':6',2 ''-terpyridine), was prepared and attached to ITO (Sn(IV)-doped In2O3) and nanocrystalline 10-20 nm diameter TiO2, ZrO2, and SnO2 thin film (similar to 10 m thickness) electrodes. The complex retains its proton-coupled electron transfer (PCET) and water oxidation properties on oxide surfaces. The electrochemically generated Ru-VI-O-Ru-V and Ru-V-O-Ru-V forms of the complex oxidize water with turnover numbers of 3.0 and 2.6 for Ru-VI-O-Ru-V and 1.8 and 1.0 for Ru-V-O-Ru-V at pH = 1 (triflic acid) and pH = 6 (terephthalic acid buffer), respectively. Cyclic voltammetric and spectroelectrochemical measurements have given significant insight into the water oxidation mechanism and origins of catalyst deactivation.