A Nickel Dithiolate Water Reduction Catalyst Providing Ligand‐Based Proton‐Coupled Electron‐Transfer Pathways

Abstract

A nickel pyrazinedithiolate ([Ni(dcpdt)2]2−; dcpdt=5,6‐dicyanopyrazine‐2,3‐dithiolate), bearing a NiS4 core similar to the active center of [NiFe] hydrogenase, is shown to serve as an efficient molecular catalyst for the hydrogen evolution reaction (HER). This catalyst shows effectively low overpotentials for HER (330–400 mV at pH 4–6). Moreover, the turnover number of catalysis reaches 20 000 over the 24 h electrolysis with a high Faradaic efficiency, 92–100 %. The electrochemical and DFT studies reveal that diprotonated one‐electron‐reduced species (i.e., [NiII(dcpdt)(dcpdtH2)]− or [NiII(dcpdtH)2]−) forms at pH<6.4 via ligand‐based proton‐coupled electron‐transfer (PCET) pathways, leading to electrocatalytic HER without applying the highly negative potential required to generate low‐valent nickel intermediates. This is the first example of catalysts exhibiting such behavior.

Electro- and Solar-Driven Fuel Synthesis with First Row Transition Metal Complexes

“…275 A similar mechanism is thought to enable the promising activity of HEC Ni23 . 277 Using a GC WE in aqueous acetate solution (pH 5.0) at E appl = −0.95 V vs SCE, Ni23 reached a TON H2 of 20 000 with >99% FE H2 over 24 h. DFT showed that only ligand-based reductions occur, along with pyrazine protonation through PCET, resulting in metal-hydride formation without low-valent Ni + or Ni 0 species. 277…”