Redox-active ligand assisted electrocatalytic water oxidation by a mononuclear cobalt complex

• Published in: Dalton transactions : an international journal of inorganic chemistry Vol. 49; no. 21; pp. 7155 - 7165
• Main Authors: Biswas, Sachidulal, Bose, Suranjana, Debgupta, Joyashish, Das, Purak, Biswas, Achintesh N
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 07.06.2020
• Subjects: Cobalt compounds; Cobalt oxides; Crystallography; Ligands; Oxidation; Reaction kinetics
• ISSN: 1477-9226; 1477-9234; 1477-9234
• DOI: 10.1039/d0dt00838a

In this report, the synthesis, characterization and electrocatalytic oxidation of water by a mononuclear cobalt( iii ) complex, [Co III (dpaq)(Cl)]Cl ( 1 ) featuring a redox-active pentadentate amidate ligand (H-dpaq = 2-[bis(pyridin-2-ylmethyl)]amino- N -quinolin-8-yl-acetamidate) is reported. Complex 1 has been found to be a stable and homogeneous water oxidation catalyst (WOC) in 0.1 M phosphate buffer (pH 8.0). A series of experiments (rinse test, SEM, EDX spectroscopy) confirm that this complex acts as a molecular electrocatalyst, and not a precursor of CoOx. The electrocatalytic water oxidation proceeds with high faradaic efficiency (81%) and fast rate (85 s −1 ). Analysis of the electrochemical reaction kinetics by foot-of-the-wave (FOWA) methodology reveals a high turnover frequency of 1.6 × 10 4 s −1 which is comparable to the best performing Ru-based WOCs. A cobalt complex bearing a redox-active monoanionic amidate ligand is shown to act as an efficient molecular electrocatalyst for water oxidation at a moderate overpotential (∼500 mV) in mildly alkaline medium.