Electrocatalytic hydrogen evolution by Co(II) complexes of bistriazolylpyridines

Two cobalt complexes [Co(L1)2](ClO4)2,4CH3CN (1) and [Co(L2)2](ClO4)2,2CH3CN,0.5H2O (2) of the new click-derived bistriazolylpyridines 2,6-bis(1-(pyridin-2-yl)-1H-1,2,3-triazol-4-yl) isonicotinate methyl ester (L1) and 2,6-bis-(1-methoxycarbonylmethyl-1H-1,2,3-triazol-4-yl)isonicotinate methyl ester (L2) were synthesized and characterized. The electrocatalytic hydrogen evolution reaction (HER) mediated by complexes 1 and 2 was studied in CH3CN in the presence of acetic acid. Both complexes catalyzed HER with low overpotentials and high Faradaic efficiencies (370 mV and 93% for 1, 300 mV and 95% for 2). The distal sub-stituents on the triazolyl moiety of the bistriazolylpyridines have apparent impacts on the redox and catalytic properties of 1 and 2. The catalytic behaviors were further studied using spectroelectrochemistry and the reductant cobaltocene. It was found that the reduction of the bistriazolylpyridines was necessary for the catalytic activity. Plausible pathways were proposed for the HER mediated by 1 and 2. This work provided some hints for the preparation of HER catalysts based on the redox-active triazolylpyridine ligands.(c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.