Impact of the hybridization form of the coordinated nitrogen atom on the electrocatalytic water oxidation performance of copper complexes with pentadentate amine-pyridine ligands.

The field of molecular catalysts places a strong emphasis on the connection between the ligand structure and its catalytic performance. Herein, we changed the type of coordinated nitrogen atom in pentadentate amine-pyridine ligands to explore the impact of its hybridization form on the water oxidation performance of copper complexes. In the electrochemical tests, the copper complex bearing dipyridine-triamine displayed an apparently higher rate constant of 4.97 s-1, while the copper complex with tripyridine-diamine demonstrated overpotential reduction by 56 mV and better long-term electrolytic stability.

A low-cost commercial Cu(II)-EDTA complex for electrocatalytic water oxidation in neutral aqueous solution.

Herein, we choose a commercial Cu complex [Cu(EDTA)(H2O)] (EDTA = ethylene diamine tetraacetic acid) as a molecular catalyst for water oxidation to avoid complex synthesis and lower catalyst cost. [Cu(EDTA)(H2O)] could catalyze the water oxidation reaction efficiently under neutral conditions with an overpotential of 684 mV, a kcat of 8.03 s-1 and good stability in the long-term electrolysis. Our finding is of great significance for the development of stable, rapid, and easily accessible catalysts for water oxidation.

Electrocatalytic water oxidation by a water-soluble copper complex with a pentadentate amine-pyridine ligand.

A water-soluble copper complex with a diamine-tripyridine ligand was synthesized successfully and well characterized. It was found to be catalytically active for the water oxidation reaction under basic conditions. Based on the electrochemical test result, this copper complex displayed an apparent rate constant (kcat) of 0.81 s-1 for the oxygen evolution reaction in 0.1 M phosphate buffer solution at pH 11.0. More importantly, the copper complex remained stable over 3 h of a bulk electrolysis experiment at 1.60 V with a Faradaic efficiency of 90.7% for O2 evolution, and the decrement of current density was only 1.9%. These results suggest that the pentadentate copper complex is an efficient and durable homogeneous Earth-abundant electrocatalyst for water oxidation.