Cobalt Carbonate as an Electrocatalyst for Water Oxidation

Co-II salts in the presence of HCO3-/CO32- in aqueous solutions act as electrocatalysts for water oxidation. It comprises of several key steps: (i) A relatively small wave at E-pa approximate to 0.71 V (vs. Ag/AgCl) owing to the Co-III/II redox couple. (ii) A second wave is observed at E-pa approximate to 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 HCO3-/CO32- to HCO4-. (iii) A process with very large currents at >1.2 V owing to the formation of Co-V(CO3)(3)(-), which oxidizes both water and HCO3-/CO32-. These processes depend on [Co-II], [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 Co-n(CO3)(3)(n-6), n=4, 5 are attainable at potentials similar to those experimentally observed.