A Thiosemicarbazone–Nickel(II) Complex as Efficient Electrocatalyst for Hydrogen Evolution

Abstract

We report herein the synthesis and characterization of a new mononuclear nickel complex based on a thiosemicarbazone ligand that exhibits an electrocatalytic behavior for H2 evolution in DMF using trifluoroacetic acid (TFA) as the proton source. Catalysis is observed at quite small overpotential values and a maximum turnover frequency (TOFmax) of 3080 s−1 was extrapolated for 1 m proton concentration using the foot‐of‐the wave analysis of cyclic voltammetry data. Gas analysis during controlled potential electrolysis experiments confirmed the catalytic nature of the process and production of dihydrogen with 80 % faradaic yield. Quantum chemical calculations indicate that the catalytic mechanism involves first ligand‐based reduction and protonation steps followed by metal‐centered processes.

Electrocatalytic H2 Evolution by the Co‐Mabiq Complex Requires Tempering of the Redox‐Active Ligand

“…Consequently, the ligands can act as reservoirs for hydrogen atoms or hydrides during the catalytic cycle. The H 2 evolution pathways of, e. g., pincer, thiosemicarbazone, and thiolate complexes are known to involve the redox‐active scaffold. Proton relay sites and redox‐active ligands are proposed to significantly enhance the kinetics of H 2 formation and decrease the HER overpotentials of metal complexes .…”

“…Alternatively, Mabiq protonation in the pre‐catalytic step may render the ligand less nucleophilic, potentially facilitating a metal‐based catalytic cycle at lower potentials. Reduction and protonation of redox active ligands preceding metal hydride formation has been observed in Ni‐thiosemicarbazone complexes . In our system, a second proton transfer in an ECEC pathway also could involve the metal center.…”

“…The H 2 evolution pathways of, e. g., pincer, thiosemicarbazone, and thiolate complexes are known to involve the redox‐active scaffold. Proton relay sites and redox‐active ligands are proposed to significantly enhance the kinetics of H 2 formation and decrease the HER overpotentials of metal complexes . However, a redox non‐innocent coordination environment also may result in non‐productive pathways .…”

Hydrogen Evolution Reactions Catalyzed by a Bis(thiosemicarbazone) Cobalt Complex: An Experimental and Theoretical Study

“…The most efficient molecular catalysts are currently based on first-row transitionm etal ions like cobalt [6][7][8][9][10] and nickel. [6,[11][12][13][14] Metal complexes based on thiosemicarbazone ligands are now emerging asan ew class of electrocatalyst for HER. [14][15][16][17] These complexes presents ome interesting features that are relevant for electrocatalytic protonreduction:the thiosemicarbazone ligand has already been shown to be redox active, [14,[18][19][20][21] whereas the presence of S-donors and severalNatoms allows for protonation of the ligand and can serve as proton relays.…”

Homogeneous ligand-centered hydrogen evolution and hydrogen oxidation : exploiting redox non-innocence to drive catalysis.

“…The NiL 2 catalyst demonstrates ligand-assisted metal reactivity that is proposed to involve initial ligand-centered reduction and protonation followed by metalcentered reduction. 88 The initial ligand reactivity allows the second reduction to occur at , which then reacts with a free proton in solution to evolve H 2 . However, due to adsorption onto the electrode surface during prolonged electrolysis when held at cathodic potentials, we cannot discount the possibility that the catalytically active species for H 2 evolution is this adsorbed film.…”