Cobalt Carbonate as an Electrocatalyst for Water Oxidation

Co II salts in the presence of HCO 3 − /CO 3 2− in aqueous solutions act as electrocatalysts for water oxidation. It comprises of several key steps: (i) A relatively small wave at E pa ≈0.71 V (vs. Ag/AgCl) owing to the Co III/II redox couple. (ii) A second wave is observed at E pa ≈1.10 V with a considerably larger current. In which the Co III undergoes oxidation to form a Co IV species. The large current is attributed to catalytic oxidation of HCO 3 − /CO 3 2− to HCO 4 − . (iii) A process with very large currents at >1.2 V owing to the formation of Co V (CO 3 ) 3 − , which oxidizes both water and HCO 3 − /CO 3 2− . These processes depend on [Co II ], [NaHCO 3 ], 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 Co n (CO 3 ) 3 n −6 , n =4, 5 are attainable at potentials similar to those experimentally observed.