Electrocatalytic H2 Evolution Promoted by a Bioinspired (N2S2)Ni(II) Complex at Low Acid Concentration

The electrochemical hydrogen evolution reaction (HER) is of great interest to advance fuel cell technologies. Although heterogeneous HER electrocatalysts are desired for practical energy devices, the development of molecular electrocatalysts is important to elucidate the mechanism and improve the activity of state-of-the-art HER catalysts. Inspired by the enzymatic HER process promoted by [NiFe] hydrogenases, we synthesized a bioinspired Ni^II electrocatalyst that produces H₂ from CF₃CO₂H at low acid concentrations (<0.043 M) in MeCN. Under these conditions, the turnover frequency for HER achieved herein is ~200,000 s^–1. We propose that our Ni^II electrocatalyst follows a novel HER mechanism by undergoing a 2e^– transfer process in a single step, followed by stepwise H⁺ transfer at low acid concentrations, while the increase in acid concentration changes the HER mechanism toward a concerted H⁺/e^– transfer. Finally, we evaluated the HER activity of our catalyst by benchmarking its kinetic and thermodynamic parameters vs. other reported HER electrocatalysts.