Energy Technologies

In this study, we report the electrocatalytic behavior of the neutral, monomeric Cu(II) complex of diacetyl-bis(N-4-methyl-3-thiosemicarbazonato), CuL¹, for metal-assisted ligand-centered hydrogen evolution in acetonitrile and dimethylformamide. CuL¹ displays a maximum turnover frequency (TOF) of 10 000 s^-1 in acetonitrile and 5100 s^-1 in dimethylformamide at an overpotential of 0.80 and 0.76 V, respectively. The rate law is first-order in catalyst and second-order in proton concentration. Gas analysis from controlled potential electrolysis confirms CuL¹ as an electrocatalyst to produce H₂ with a minimum Faradaic efficiency of 81% and turnover numbers as high as 73 while showing no sign of degradation over 23 h. The H₂ evolution reaction (HER) was probed using deuterated acid, demonstrating a kinetic isotope effect of 7.54. A proton inventory study suggests one proton is involved in the rate-determining step. Catalytic intermediates were identified using ¹H NMR, X-ray photoelectron, and UV-visible spectroscopies. All catalytic intermediates in the proposed mechanism were successfully optimized using density functional theory calculations with the B3LYP functional and the 6-311g(d,p) basis set and support the proposed mechanism.