Molecular Cobalt Complexes with Pendant Amines for Selective Electrocatalytic Reduction of Carbon Dioxide to Formic Acid

Abstract

We report here on a new series of CO-reducing molecular catalysts based on Earth-abundant elements that are very selective for the production of formic acid in dimethylformamide (DMF)/water mixtures (Faradaic efficiency of 90 ± 10%) at moderate overpotentials (500-700 mV in DMF measured at the middle of the catalytic wave). The [CpCo(PN)I] compounds contain diphosphine ligands, PN, with two pendant amine residues that act as proton relays during CO-reduction catalysis and tune their activity. Four different PN ligands with cyclohexyl or phenyl substituents on phosphorus and benzyl or phenyl substituents on nitrogen were employed, and the compound with the most electron-donating phosphine ligand and the most basic amine functions performs best among the series, with turnover frequency >1000 s. State-of-the-art benchmarking of catalytic performances ranks this new class of cobalt-based complexes among the most promising CO-to-formic acid reducing catalysts developed to date; addressing the stability issues would allow further improvement. Mechanistic studies and density functional theory simulations confirmed the role of amine groups for stabilizing key intermediates through hydrogen bonding with water molecules during hydride transfer from the Co center to the CO molecule.

Solvent and Ligand Substitution Effects on the Electrocatalytic Reduction of CO2 with [Mo(CO)4(x,x′‐dimethyl‐2,2′‐bipyridine)] (x=4–6) Enhanced at a Gold Cathodic Surface

“…Currently, much of the literature regarding molecular electrochemical activation of CO 2 still continues to explore the catalytic properties of the heavier members of Group‐7 (Re), Group‐8 (Ru and Os) and Group‐9 (Rh, and Ir) triads. These “first‐generation” electrocatalysts must be phased out; encouragingly, cheaper alternatives exist within the same groups – Mn substituting Re, Fe substituting Ru and Os, and Co substituting Rh and Ir . However, the community's focus on late transition metals is leaving the Group‐6 metals (Cr, Mo, W) rather neglected, despite the high potential for the comparatively abundant metal triad to function as both high‐performance alternatives to the noble metals and photostable alternatives to the hot‐topic manganese carbonyls .…”

Recent Trends, Benchmarking, and Challenges of Electrochemical Reduction of CO2 by Molecular Catalysts

“…[64][65][66][67] This is because existing cobalt molecular catalysts perform very well in organic solvents when reducing CO 2 ; however, in aqueous environments, cobalt selectively promotes proton reduction and generates HER. [64][65][66][67] This is because existing cobalt molecular catalysts perform very well in organic solvents when reducing CO 2 ; however, in aqueous environments, cobalt selectively promotes proton reduction and generates HER.…”

“…[77] As previously reported, [75] solution-phase hybridization of cobalt phthalocyanine and MWCNT (in addition to carbon black and graphene) was adopted to modify the electrodes. [78] In 2017, inspired from the catalyst design of the aforementioned Co-aminopyridine macrocycle, [78] Roy et al [67] extended the structures to form a novel family of Co complexes with pendant amines present in diphosphine ligands, P R 2 N R' 2. CPE on a CO 2 saturated aqueous media yielded a TON CO of 97 000 with FE CO of ≈90% at E appl = −0.63 V versus RHE for 10 h. Substitution in the molecular structure with electron-withdrawing cyano groups resulted in a high FE CO of 98% at E appl = −0.63 V versus RHE and negligible current decay over an hour, demonstrating the possibility of catalyst tuning through modification of electronic properties.…”

“…[67] In order to understand the reduction mechanism of CO 2 , surface immobilized CoPP electrodes (CoPP-PG) were produced with the porphyrins forming a flat monolayer on the electrode surface with a high coating area. [67] In order to understand the reduction mechanism of CO 2 , surface immobilized CoPP electrodes (CoPP-PG) were produced with the porphyrins forming a flat monolayer on the electrode surface with a high coating area.…”

MoP Nanoparticles Supported on Indium‐Doped Porous Carbon: Outstanding Catalysts for Highly Efficient CO2 Electroreduction

“…[3,4] The electricity used to drive the processes can be generated from renewable energy sources,such as solar and wind. [6][7][8][9][10][11][12][13][14][15][16] Although these electrodes show competent CO 2 reduction performances,t hey usually suffer from limited availability and low efficiency. [6][7][8][9][10][11][12][13][14][15][16] Although these electrodes show competent CO 2 reduction performances,t hey usually suffer from limited availability and low efficiency.…”