Hydrogen evolution by cobalt tetraiminecatalysts adsorbed on electrode surfaces

Abstract

Aryl-substituted tetraimine complexes related to Co(dmgBF 2 ) 2 -(MeCN) 2 (dmg = dimethylglyoxime) were synthesized and are active for hydrogen evolution. Co(dmgBF 2 ) 2 (MeCN) 2 can be adsorbed to a glassy carbon electrode. The chemically modified electrode is active for hydrogen evolution in aqueous solution at pH o 4.5, with an overpotential of only 100 mV.Developing efficient hydrogen evolution catalysts composed of earth-abundant materials is of considerable current interest. 1 Recent work has established that cobalt tetraimine macrocyclic complexes such as Co(dmgBF 2 ) 2 (MeCN) 2 (dmg = dimethylglyoxime) (1) 2 can function as efficient electrocatalysts for the production of hydrogen from protons. [3][4][5] These systems are attractive because they operate at low overpotentials and at potentials that are quite positive relative to previously explored Co and Ni macrocycle systems. Nickelphosphine and cobalt systems pioneered by the DuBois lab are of similar interest. 6 Because the ultimate use of such electrocatalysts in a H 2 -evolving device will likely require grafting them to an electrode surface, we sought to ascertain whether these cobalt catalysts would still function once tethered to an electrode, and how their respective stabilities would be impacted. [7][8][9] Related surface studies have utilized a Nafion membrane to obtain a functional electrode-catalyst system. 10 Derivatization of tetraimine-based macrocycles with the form of 1 is not very versatile due to the metal-templated method used in the ligand's synthesis. We have therefore examined a ligand related to a known Schiff base/oxime tetraimine construct, 11 for which the ligand can be preformed before addition of cobalt. Herein, we report that these tetraimine cobalt complexes can be used to prepare chemically modified electrodes from indium tin oxide (ITO)-coated glass that are active for hydrogen evolution. We moreover establish that 1 is a substantially better hydrogen-evolving catalyst in aqueous solution once attached to a glassy carbon (GC) electrode.Access to various aryl-substituted tetraimine complexes related to 1 was achieved via a two-step synthesis involving initial isolation of the proton-linked glyoxime tetraimine followed by generation of the BF 2 -linked analogue (see Fig. 1 for labeling scheme and ESIw for synthetic details). 12 Solid-state structures were obtained for compounds 3-6 and 8 (Fig. S1).w

Co@NH2-MIL-125(Ti): cobaloxime-derived metal–organic framework-based composite for light-driven H2 production

“…(DOH)pn), previously employed as electrocatalyst for proton reduction, 48,49 as molecular guest to demonstrate our concept 50,51 illustrated in Scheme 2:…”

Structural and electronic characterization of multi-electron reduced naphthalene (BIAN) cobaloximes

“…9 The various stages of cobaloxime catalysis have been investigated by electrochemical methods, [10][11][12][13] density functional theory, [14][15][16] electron paramagnetic spectroscopy, 17 and photophysical techniques. 18,19 Cobaloximes have also been incorporated into heterogeneous systems such as glassy carbon, 20 nickel oxide, 21 carbon nanotubes, 22 and gallium phosphide 23,24 substrates. Furthermore, cobaloximes have been explored in conjunction with homogeneous photosensitizers, [25][26][27][28] as components in aqueous systems, [29][30][31] as a functional catalyst on vesicle membrane surfaces, 32 and used as part of an artificial hydrogenase in a hybrid SwMb system.…”

Catalytic hydrogen evolution from a covalently linked dicobaloxime

“…It follows that immobilization onto an electrode surface would disfavor this pathway (7,22,23). It is of interest in this context that binuclear analogues of many catalysts that rely on bimetallic interactions show enhanced activity when compared to monomeric species, examples include certain Ru and Os diporphyrin H 2 evolving catalysts with cofacial orientation (24,25).…”