Determination of the stability constant of cobalt-substituted mono-lacunary Keggin-type polyoxometalate and its electrocatalytic water oxidation performance

The anion form of a cobalt substituted mono-lacunary Keggin type polyoxometalate (POM) complex in aqueous solution was identified as [Co(H2O)(H3PW11O39)]2− and its stability constant was determined to be 5.19 × 104 by spectrophotometry. Additionally, the electrocatalytic performances towards water oxidation of different concentrations of [Co(H2O)(H3PW11O39)]2− were investigated in the neutral phosphate buffer solution, and it was found that [Co(H2O)(H3PW11O39)]2− anion itself has little activity; the activity of [Co(H2O)(H3PW11O39)]2− solution actually results from dissociated [Co(H2O)6]2+. This work provides a simple way to understand the origin of catalytic water oxidation activity of a POM-based complex.