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

Abstract

An inherent problem stalling the development of a H2-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. H2 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 ≫108 and a Faradaic efficiency > 95%. Even at pH 2, that is, [H]+ = 0.01 N, Icat/[τ] > 400 s–1 is obtained. The catalyst can be immobilized on cheap carbon electrodes, used in domestic Zn-Carbon dry batteries, to generate H2 from acid aqueous solutions.