A molecular (NCS2)Ni(II) electrocatalyst resembles [NiFe]hydrogenase pathway for H2 evolution

The electrochemical hydrogen evolution reaction (HER) is considered a sustainable energy approach to advance fuel-cell technologies, and HER electrocatalysts that resembles the [NiFe] hydrogenases are highly desired. Herein, we report a bioinspired Ni(II) complex (NCHS2)Ni(OTf)2, where NCHS2 is 3,7-dithia-1(2,6)-pyridina-5(1,3)-benzenacyclooctaphane, that is an efficient electrocatalyst for HER with turnover frequencies up to 400,000 s–1 in the presence of low acid concentration, and compares favorably with the other reported Ni HER electrocatalysts. Importantly, in this complex the rationally designed NCHS2 ligand undergoes C-H bond activation and the resulting organometallic Ni-aryl complex restricts the formation of a Ni(0) species, which resembles the role of the cysteine ligands in [NiFe] hydrogenases. In addition, this electrocatalyst follows a unique HER mechanism via detectable Ni(I)/Ni(III) intermediates that are also proposed for [NiFe] hydrogenases, yet such a mechanism has not been observed to date in model systems.