A bi-functional cobalt-porphyrinoid electrocatalyst: balance between overpotential and selectivity

Cobalt porphyrins have been shown to electrocatalyze O-2 reduction as well as H-2 evolution. A cobalt porphyrin is synthesized when two electron-withdrawing groups are used in an attempt to reduce the overpotential involved in O-2 reduction and H-2 evolution. The results show that in the case of O-2 reduction, instead of reduction of overpotential, the selectivity for O-2 reduction changes to 2e(-)/2H(+) to produce H2O2. In the case of H-2 evolution, the Co-I state is incapable of catalyzing H+ reduction. Rather, a Co-III-H species needs to be reduced to Co-II-H before H-2 can be produced. There results add to the ongoing investigations into the factors that control the rates, overpotential and selectivity of these important cathodic processes.