Studies of Cobalt-Mediated Electrocatalytic CO₂Reduction Using a Redox-Active Ligand

Abstract

The cobalt complex [CoIIIN4H(Br)2]+ (N4H = 2,12-dimethyl-3,7,11,17-tetraazabicyclo-[11.3.1]-heptadeca-1(7),2,11,13,15-pentaene) was used for electrocatalytic CO2 reduction in wet MeCN with a glassy carbon working electrode. When water was employed as the proton source (10 M in MeCN), CO was produced (fCO= 45% ± 6.4) near the CoI/0 redox couple for [CoIIIN4H(Br)2]+ (E1/2 = −1.88 V FeCp2+/0) with simultaneous H2 evolution (fH2= 30% ± 7.8). Moreover, we successfully demonstrated that the catalytically active species is homogeneous through the use of control experiments and XPS studies of the working glassy-carbon electrodes. As determined by cyclic voltammetry, CO2 catalysis occurred near the formal CoI/0redox couple, and attempts were made to isolate the triply reduced compound (“[Co0N4H]”). Instead, the doubly reduced (“CoI”) compounds [CoN4] and [CoN4H(MeCN)]+ were isolated and characterized by X-ray crystallography. Their molecular structures prompted DFT studies to illuminate details regarding their electronic structure. The results indicate that reducing equivalents are stored on the ligand, implicating redox noninnocence in the ligands for H2 evolution and CO2 reduction electrocatalysis.

Tracking the Structural and Electronic Configurations of a Cobalt Proton Reduction Catalyst in Water

“…These findings are supported by reported X-ray diffraction structures and calculations of similar intermediates for the CO 2 and proton reduction reactions. 52,53 Since the Co(II) species slowly interacts with the ascorbate ion with time, the difference spectra considering a "laser-off" Co(II) square pyramidal with coordinated ascorbate ([LCo(Asc)] + ) are also shown in Figure S10. 3 ] 2+ /Asc, corresponding to the formation and decay of the Co(III) photo-induced species (red dots) with the corresponding kinetics fitting (black solid line).…”

Proton–hydride tautomerism in hydrogen evolution catalysis

“…A case in point features ligand-centered protonation and subsequent hydride-like reactivity of a nascent C-H bond in a nickel phlorin system (16), although a nickel hydride was not implicated in the cycle for hydrogen evolution. In other work of note, Hull et al (17) reported dehydrogenation of HCO 2 H promoted by proton-responsive hydroxybipyridine-ligated catalysts, and Lacy et al (18) showed that ligand-centered protonation of a cobalt complex could lead to hydrogen evolution.…”

Organic, Organometallic and Bioorganic Catalysts for Electrochemical Reduction of CO2

“…Although various molecular catalysts (porphyrins, corroles, cyclams, naphthyridines, and so forth) with metal centers such as Pd, Ru, Fe, Co, and Ni were investigated,31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49 in the years after the discovery of Lehn's catalyst, most research has been focused on Re‐containing complexes. With an estimated average concentration of 1 ppb, Re, together with other noble metals, is one of the rarest elements in Earth's crust.…”