Water-splitting reactions in which hydrogen is produced are widely studied because of their high potential as a source of clean energy. Central to this reaction is the electrochemical production of oxygen from water. This reaction requires high overpotentials, thus different catalysts such as organometallic complexes of Ir, Pt, Rh and Ru, were developed. These complexes are some of the most active water oxidation catalysts known, but not widely used due to the high cost of production. This led to the investigation of metal oxide complexes based on earth abundant metals, including nickel–iron oxides, cobalt oxides, and cobalt phosphates (Co-Pi). These catalysts still have limitations however, such as the complicated and expensive synthesis, activity only at low/high pH values, among others. Different mechanisms for oxygen evolution by cobalt oxides, based on theoretical investigations, were recently suggested by several groups (1,2). Fernando and Aikens have suggested reaction pathways for water oxidation to molecular oxygen using simple model for the cobalt oxide dimer and cubane catalysts. Anastas and co-workers (3) have reported synthesis of a novel material from dicobalt octacarbonyl and 1,2-bis(diphenylphosphino)ethane (dppe), which was found to be an active and robust heterogeneous catalyst for electrochemical oxygen production. The resulting material is a highly amorphous substance, and its exact structure has not been determined; available compositional and structural information indicate that synthesized complex is not simple cobalt oxide or Co–Pi catalyst. Comparison of relative activity of Co-dppa, Co–Pi and Co3O4 in &lt;span style="line-height:20.8px"&gt;borate&lt;/span&gt; and &lt;span style="line-height:20.8px"&gt;phosphate&lt;/span&gt; electrolytes showed that the mode of action of Co-dppa is unique, and that dppa ligand probably plays important role in the catalysis. To explore the possible mechanisms of the catalysis using Co-dppa, we performed DFT calculations. Model systems have a cobalt dimer with the dppe ligand bridging two metal centers as a main motif. (1) Li, X.; Siegbahn, P. E. M. J. Am. Chem. Soc. 2013, 135, 13804−13813 (2) Fernando, A. and Aikens, C. M. J. Phys. Chem. C 2015, 119, 11072−110853 (3) Bloomfield, A. J.; Sheehan, S. W.; Collom, S. L.; Crabtree, R. H. and Anastas, P. T. New J. Chem. 2014, 38, 1540-1545

Water oxidation pathways using a cobalt oxide dimer catalyst

251st National Meeting (2016)

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