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 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.

阻碍氢基全球能源经济发展的固有难题，在于缺乏可在水相介质中稳定运作的高效功能催化剂。本研究针对一款铁铁氢化酶（Fe–Fe hydrogenase）模拟物，探究其在水相介质中的电催化产氢性能。将该铁铁氢化酶模拟物固定于石墨表面后，可从pH<3的酸性水溶液中制备氢气。已知此类催化剂在有机溶剂中需于极负电位下还原氢离子；而在水相介质中，其氢离子还原电位显著正移。该催化剂在相对于标准氢电极（NHE）的-0.5 V电位下，转换频率可达6400 s⁻¹，起始电位为-0.36 V。长时间电解测试表明，该催化剂的转换数远大于10⁸，法拉第效率超过95%。即便在pH=2（即氢离子浓度为0.01当量浓度）的条件下，仍可获得Icat/[τ] > 400 s⁻¹的性能参数。该催化剂可固定于民用锌碳干电池所用的廉价碳电极之上，从而从酸性水溶液中制备氢气。