Nickel(Ii) and Copper(Ii) Complexes Containing Bis(2-Pyridylmethyl)-2,2’-Thiodiethanethiol Ligands for Electro- and Photocatalytic Hydrogen Production from Water

Abstract

In this study, we synthesized and characterized two complexes: the bis(2-pyridylmethyl)-2,2’-thiodiethanethiol (bptde) ligand and its corresponding complexes [Ni(bptde)(ClO4)2] 1 and [Cu(bptde)(ClO4)2] 2. Furthermore, we systematically examined the catalytic performances of these complexes in homogeneous electrochemical and photochemical hydrogen evolution reaction. Under an overpotential (OP) of 837.6 mV, both [Ni(bptde)(ClO4)2] 1 and [Cu(bptde)(ClO4)2] 2 demonstrated electrocatalytic activity for the hydrogen evolution reaction (HER) in neutral buffer solution with corresponding turnover frequencies (TOFs) were 1372 h-1 and 478 h-1, respectively. In terms of photocatalysis, 1 demonstrated continuous catalysis for water reduction for 60 h with a total turnover number (TON) of 19676 mol H2 (mol cat)-1, while maintaining an average apparent quantum yield (AQY) of approximately 19.86%. On the other hand, during 36 h irradiation period, [Cu(bptde)(ClO4)2] 2 achieved a TON value of 1542 mol H2 (mol cat)-1, with an average AQY of approximately 4.71%. The experimental findings indicated that the nickel complex exhibited significantly superior catalytic activity compared to the copper complex with the identical ligand, bptde. This study not only presents a novel perspective on the design of molecular catalysts for the hydrogen evolution reaction (HER) but also suggests cost-effective alternatives for precious metals in H2 production.

Keywords: complexes, homogeneous electrocatalyst, photocatalysts, hydrogen evolution, water reduction rection