Electrochemical Hydrogen Production in Acidic Water by an Azadithiolate Bridged Synthetic Hydrogenese Mimic: Role of Aqueous Solvation in Lowering Overpotential

An inherent problem stalling the development of a H 2 -based global energy economy is the unavailability of efficient functional catalysts that can function in aqueous media. A Fe–Fe hydrogenase mimic is investigated for electrocatalytic hydrogen generation in aqueous medium. H 2 is produced from acid water (pH <3) by a Fe–Fe hydrogenase mimic immobilized on graphite surfaces. These catalysts are known to reduce H + at very negative potentials in organic solvents. However, in aqueous medium, the H + reduction potential is shifted to much more positive values. The catalyst shows a turnover frequency of 6400 s –1 at −0.5 V and an onset potential of −0.36 V vs NHE. Prolonged electrolysis shows that the catalyst has a turnover number ≫10 8 and a Faradaic efficiency > 95%. Even at pH 2, that is, [H] + = 0.01 N, I cat /[τ] > 400 s –1 is obtained. The catalyst can be immobilized on cheap carbon electrodes, used in domestic Zn-Carbon dry batteries, to generate H 2 from acid aqueous solutions.