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A variety of metal oxides can catalyze the oxidation of water to molecular oxygen when polarized by a sufficiently high electrochemical potential. Minimizing the overpotential and increasing the rate of the oxygen-evolving reaction (OER) are key goals in making such materials a component of viable energy storage devices. However, the structural factors that imbue the metal oxides with their catalytic power are difficult to assess as these solids contain many distinct metal-ion sites, have a varying amount of defect sites within the lattice, and can be composed of multiple phases. In the present study, we determined the magnetic properties for a series of dimeric cobalt complexes in which the two metal centers are bridged by a dioxygen moiety. Our spectroscopically validated electronic structure description indicates that each species is best described as two Co(III) ions that are bound to a μ–η1η1 superoxide ligand. Intriguingly, we found evidence that the two compounds that possess oxygen-evolving activi...

Thin-film water oxidation catalysts (Co-Pi) prepared by electrodeposition from phosphate electrolyte and Co(NO(3))(2) have been characterized by electron paramagnetic resonance (EPR) spectroscopy. Co-Pi catalyst films exhibit EPR signals corresponding to populations of both Co(II) and Co(IV). As the deposition voltage is increased into the region where water oxidation prevails, the population of Co(IV) rises and the population of Co(II) decreases. The changes in the redox speciation of the film can also be induced, in part, by prolonged water oxidation catalysis in the absence of additional catalyst deposition. These results provide spectroscopic evidence for the formation of Co(IV) species during water oxidation catalysis at neutral pH.