Rapid Water Reduction to H2 Catalyzed by a Cobalt Bis(iminopyridine) Complex

A cobalt bis(iminopyridine) complex is a highly active electrocatalyst for water reduction, with an estimated apparent second order rate constant k(app) <= 10(7) M-1 s(-1) over a range of buffer/salt concentrations. Scan rate dependence data are consistent with freely diffusing electro-active species over pH 4-9 at room temperature for each of two catalytic reduction events, one of which is believed to be ligand based. Faradaic H-2 yields up to 87 +/- 10% measured in constant potential electrolyses (-1.4 V vs SCE) confirm high reactivity and high fidelity in a catalyst supported by the noninnocent bis(iminopyridine) ligand. A mechanism involving initial reduction of Co2+ and subsequent protonation is proposed.