Catalytic water oxidation mediated by copper‐triazolylpyridine complexes

Abstract

Water oxidation reaction (WOR) is a rather sluggish process in the water splitting that hampers the extraction of hydrogen gas from water in a large scale. It is highly desirable to develop low‐cost WOR catalysts to increase the efficacy. Herein two Cu(II) complexes [Cu (DTEL)2]n(ClO4)2n (1) and [Cu(DTE)2(ClO4)2] (2) of two triazolylpyridines, 1‐(2‐hydroxy)‐4‐(2‐pyridyl)1,2,3‐triazole (DTEL) and 1‐(2‐acetoxymethyl)‐4‐(2‐pyridyl)1,2,3‐triazole (DTE), have been synthesized and characterized. The X‐ray diffraction analysis revealed that the copper centers of 1 and 2 adopted the octahedral coordination geometry with four N atoms from two DTEL or DTE ligands in the equatorial plane. The two axial sites were weakly ligated by the hydroxyl group of DTEL or perchlorate. Both complexes 1 and 2 were homogenous molecular catalysts boosting the WOR in pH 9.0 phosphate buffer solution with the overpotentials being 568 and 478 mV, rate constants (kcat) of 0.1 and 0.39 s−1, and Faradaic efficiencies of 90% and 93%, respectively. The pendant substituent on the two triazolylpyridine ligands DTEL and DTE apparently influenced the catalysis. A mechanism for the catalytic WOR mediated by 1 and 2 was suggested on the basis of the experimental data. This work illustrated that triazolylpyridines were promising scaffolds for forming metal complexes working as WOR catalysts.

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

“…4,5 Up to now, more than 60 types of copper complexes with various ligand structures have been reported as electrocatalysts for water oxidation, showing different catalytic performance. 6–30 Llobet and co-workers reported a series of copper complexes with amide tetradentate ligands. 6 When two methoxy groups were introduced to the phenyl group, the overpotential was as low as 170 mV.…”

“…7 In contrast, the TOF of a majority of copper catalysts is below 10 s −1 . 19–27 In addition, the binuclear copper complex reported by Wang's group showed excellent stability and a high Faraday efficiency of 97% in electrolysis over 16 h. 30 However, current attenuation and even the deposition phenomenon occurred in some catalysts during the process of electrolysis. 11,15,20,31 The existing copper molecular catalysts display obvious differences in their performance in water oxidation primarily due to the ligand structure.…”