An all-inorganic, oxidatively and thermally stable, homogeneous water oxidation catalyst based on redox-active (vanadate(V)-centered) polyoxometalate ligands, Na-10[Co-4(H2O)(2)(VW9O34)(2)]center dot 35H(2)O (Na(10)1-V2, sodium salt of the polyanion 1-V2), was synthesized, thoroughly characterized and shown to catalyze water oxidation in dark and visible-light-driven conditions. This synthetic catalyst is exceptionally fast under mild conditions (TOF > 1 x 10(3) s(-1)). Under light-driven conditions using [Ru(bpy)(3)](2+) as a photosensitizer and persulfate as a sacrificial electron acceptor, 1-V2 exhibits higher selectivity for water oxidation versus bpy ligand oxidation, the final 02 yield by 1-V2 is twice as high as that of using [Co-4(H2O)(2)(PW9O34)(2)](10-) (1-P2), and the quantum efficiency of O-2 formation at 6.0 mu M 1-V2 reaches similar to 68%. Multiple experimental results (e.g., UV-vis absorption, FT-IR, V-51 NMR, dynamic light scattering, tetra-n-heptylammonium nitrate-toluene extraction, effect of pH, buffer, and buffer concentration, etc.) confirm that the polyanion unit (1-V2) itself is the dominant active catalyst and not Co2+(aq) or cobalt oxide.