Electrocatalytic CO reduction by a cobalt porphyrin mini-enzyme.

Cobalt-mimochrome VIa (CoMC6a), a synthetic mini-enzyme with a cobalt porphyrin active site, is developed as a biomolecular catalyst for electrocatalytic CO reduction in water. The catalytic turnover number reaches ∼14 000 for CO production with a selectivity of 86 : 5 over H production under the same conditions. Varying the applied potential and the p of the proton donor was used to gain insight into the basis for selectivity. The protected active site of CoMC6a is proposed to enhance selectivity for CO reduction under conditions that typically favor H production by related catalysts. CoMC6a activity and selectivity change only marginally under air, indicating excellent oxygen tolerance.