Electrochemical water oxidation catalyzed by a mononuclear cobalt complex of a pentadentate ligand: the critical effect of the borate anion

• Published in: New journal of chemistry 2022-04, Vol.46 (16), p.7522-7527
• Main Authors: Zheng, Haixia, Ye, Hui, Xu, Tao, Zheng, Kaibo, Xie, Xinyi, Zhu, Binghui, Wang, Xichao, Lin, Junqi, Ruan, Zhijun
• Format: Article
• Language: English
• Subjects: Buffer solutions; Catalytic activity; Cobalt; Cobalt compounds; Cobalt oxides; Coordination compounds; Electron transfer; Hydroxides; Oxidation; Protons
• ISSN: 1144-0546; 1369-9261
• DOI: 10.1039/d2nj01154a

Electrochemical water oxidation catalyzed by a cobalt complex, [Co(N3Py2)(H 2 O)] (ClO 4 ) 2 ( 1 ) (N3Py2 = 2,5,8-trimethyl-1,9-bis(2-pyridyl)-2,5,8-triazanonane), is reported. The release of dioxygen (O 2 ) occurs with a moderate onset overpotential of 540 mV and turnover frequency ( k cat ) of 0.79 s −1 . Collective experimental results confirm that 1 homogeneously catalyzes water oxidation without undergoing decomposition into cobalt oxides or cobalt hydroxides. Detailed electrochemical investigation clarified the mechanism of water oxidation, indicating that the implementation of a proton-coupled electron transfer (PCET) process and the formation of an O-O bond in the catalytic cycle are assisted by the ion of the buffer solution. Compared to hydrogen phosphate, borate, which is more receptive to protons, leads to a more remarkable catalytic activity. This work suggests that the buffer solution may have a critical effect on the catalytic performance of metal complexes. The disclosed information is expected to inspire new ideas for the development of efficient homogeneous complex catalysts for water oxidation. A cobalt complex is found as a homogeneous water oxidation electrocatalyst. Electrochemical examinations indicate that the implementation of proton-couple electron transfer process and formation of O-O bond are assisted by borate anion.