Cobalt porphyrins as homogeneous catalysts for water oxidation

Three water-soluble cobalt porphyrins have been investigated as water oxidation catalysts via photo-initiation using Ru-II(bpy)(3)(2+)/Na2S2O8. The pH dependence of the turnover frequency revealed maximum activity at pH 11. Based on the second order dependence on catalyst concentration for the rate of water oxidation, we suggest a bimolecular radical coupling process as the rate determining step.