Cobalt Carbonate as an Electrocatalyst for Water Oxidation.

CoII salts in the presence of HCO3 - /CO3 2- in aqueous solutions act as electrocatalysts for water oxidation. It comprises of several key steps: (i) A relatively small wave at Epa ≈0.71 V (vs. Ag/AgCl) owing to the CoIII/II redox couple. (ii) A second wave is observed at Epa ≈1.10 V with a considerably larger current. In which the CoIII undergoes oxidation to form a CoIV species. The large current is attributed to catalytic oxidation of HCO3 - /CO3 2- to HCO4 - . (iii) A process with very large currents at >1.2 V owing to the formation of CoV (CO3 )3 - , which oxidizes both water and HCO3 - /CO3 2- . These processes depend on [CoII ], [NaHCO3 ], and pH. Chronoamperometry at 1.3 V gives a green deposit. It acts as a heterogeneous catalyst for water oxidation. DFT calculations point out that Con (CO3 )3 n-6 , n=4, 5 are attainable at potentials similar to those experimentally observed.