LAUSR

Abstract Two nickel(II) complexes [Ni(L1)2]Br2 and [Ni(L2)2]Br2 (HL1Cl = 1-benzyl-3-(pyridin-2-ylmethyl)benzimidazolium chloride; HL2Cl = 1,3-bis(pyridin-2-ylmethyl)benzimidazolium chloride) were synthesized as non-noble metal catalysts for the electrocatalytic hydrogen evolution reaction. Single crystal X-ray crystallography revealed that the nickel metal centers in both compounds are in a square-planar geometry with like donor atoms of the two bidentate ligands in cis positions. The redox properties of the two compounds were studied using cyclic voltammetry. Electrocatalytic proton reduction experiments using these complexes were performed in DMF with acetic acid as the proton source. Compound [Ni(L2)2]Br2, containing two free pyridyl groups, not only exhibits higher electrocatalytic activity, but also has a smaller overpotential for the reduction of protons. The comparison of these results provides convincing experimental evidence for the pyridyl group acting as proton relay during the proton reduction process, although unfortunately the performance of the compounds is rather low.