Immobilization of “Capping Arene” Cobalt(II) Complexes on Ordered Mesoporous Carbon for Electrocatalytic Water Oxidation

Abstract

We report the synthesis, characterization, and electrocatalytic water oxidation activity of two cobalt complexes, (6-FP)Co(NO 3 ) 2 (1) (6-FP = 8,8′-(1,2phenylene)diquinoline) and (5-FP)Co(NO 3 ) 2 (2) (5-FP = 1,2-bis(N-7-azaindolyl)benzene), containing "capping arene" bidentate ligands with nitrogen atom donors. The cobalt complexes 1 and 2 were supported on ordered mesoporous carbon (OMC) by π−π stacking, resulting in heterogenized cobalt materials 6-FP-Co-OMC-1 and 5-FP-Co-OMC-2, respectively, and studied for electrocatalytic water oxidation. We find that 6-FP-Co-OMC-1 exhibits an overpotential of 355 mV for a current density of 10 mA cm −2 and a turnover frequency (TOF) of ∼0.53 s −1 at an overpotential of 400 mV at pH 14. 6-FP-Co-OMC-1 exhibits activity that is ∼1.6 times that of 5-FP-Co-OMC-2, which gives a TOF of 0.32 s −1 at 400 mV overpotential. The structural stability of the single-atom Co site was demonstrated for 6-FP-Co-OMC-1 using X-ray absorption spectroscopy for the molecular complex supported on OMC, but slow degradation in catalyst activity can be attributed to eventual formation of Co oxide clusters. DFT computations of electrocatalytic water oxidation using the molecular complexes as models provide a description of the catalytic mechanism. These studies reveal that the mechanism for O−O bond formation involves an intermediate Co IV oxo complex that undergoes an intramolecular reductive O−O coupling to form a Co II − OOH species. Further, the calculations predict that the molecular 6-FP-Co structure is more active for electrocatalytic water oxidation than 5-FP-Co, which is consistent with experimental studies of 6-FP-Co-OMC-1 and 5-FP-Co-OMC-2, highlighting the possibility that the ligand structure influences the catalytic activity of the supported molecular catalysts.

Cobalt Electrocatalyst on Fluorine Doped Carbon Cloth – a Robust and Partially Regenerable Anode for Water Oxidation

“…Benchmarking these catalytic systems is challenging as different electro-materials are investigated under different reaction conditions. [44] In order to allow the comparison with our CoPFCC system, we chose those cobalt-containing catalysts that were tested on the heterogeneous surface under near neutral pH using phosphate buffer. We also preferred to calculate an average TOF value over a long oxidation experiment rather than an initial TOF value.…”

Pyridinic Nitrogen Sites Dominated Coordinative Engineering of Subnanometric Pd Clusters for Efficient Alkynes’ Semihydrogenation

“…[ 1–6 ] Among them, one of the most important but challenging reactions is the alkynes’ semihydrogenation to corresponding alkenes because of their poor alkene selectivity due to excessive hydrogenation and desorption barriers of alkenes, especially when the conversion is high. [ 7–10 ] The current problem‐solving technique mainly relies on the development of diverse supported metal catalysts, [ 11–14 ] while the precondition is to exploit available support material that can stabilize and promote the active metal sites to own outstanding catalytic activity and selectivity for the semihydrogenation of alkynes.…”

Processing Poly (ethylene terephthalate) Waste into Functional Carbon Materials by Mechanochemical Extrusion

“…[12,13] Mo 2 C nanoparticles are also chosen for their abundance of dband electrons, which may promote the nucleophilicity of nanocarbon. Besides metal carbides, transition metallic species are often supported on mesoporous carbon for various catalytic processes (e. g., hydrogenation, [14] cross-coupling reaction, [15] Fischer-Tropsch process, [16] oxygen reduction reaction, [17] electrochemical water splitting [18] ). Moreover, carbon-supported transition metal catalysts are attractive due to their low cost and abundant reserves.…”