Enhancing the electrochemical capacitor performance of Keggin polyoxometalates by anchoring cobalt-triazole complexes

• Published in: Journal of molecular structure 2022-02, Vol.1250, p.131753, Article 131753
• Main Authors: Hu, Sumin, Li, Kunqi, Yu, Xiaojing, Jin, Zhongxin, Xiao, Boxin, Yang, Ruoru, Pang, Haijun, Ma, Huiyuan, Wang, Xinming, Tan, Lichao, Yang, Guixin
• Format: Article
• Language: English
• Subjects: Keggin; Polyoxometalate; Sandwiched structure; Supercapacitor
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/j.molstruc.2021.131753

•Intriguing polyoxometalate-sandwiched porous structures.•Exhibiting high specific capacitance and long cycling stability.•The capacitance is 1.5 times higher than that of parental POM.•Improving the electrochemical performance of pure POMs. Polyoxometalate (POM)-based coordination hybrids not only integrate the benefits of POMs and transition-metal complexes perfectly, but also ameliorate the demerits of individual components, providing a prospective strategy to approach high performance supercapacitors. In this work, two new coordination hybrids [CoII(pzta)2(H2O)]2(H4GeMo12O40)·4H2O (1), and [CoII(pzta)2(H2O)]2(H4SiMo12O40)·4H2O (2), (3-pyrazinyl-1, 2, 4-triazole = pzta) were synthesized by a hydrothermal method. The structures were determined by single-crystal X-ray diffraction analyses and further confirmed by IR, PXRD and XPS techniques. Compounds 1 and 2 are isostructural compounds that only differ in the central atom of the Keggin clusters possessing POM-sandwiched porous structures. The electrochemical properties including cyclic voltammetry, galvanostatic charge-discharge, electrochemical active surface area, and electrochemical impedance spectroscopy of 1- and 2-based electrodes in the three-electrode system were studied in details. The results of electrochemical tests indicate that these electrodes possess high specific capacitance and good cycling stability. When the current density is 1 A g−1, the specific capacitance is 121.5 F g−1 for 1-based electrode, 182.0 F g−1 for 2-based electrode, 121.5 Fg−1 for [SiMo12O40]-based electrode and 46.2 Fg−1 for Co-pzta-based electrode. Therefore, the specific capacitance of 2-based electrode 1.5 times higher than that of parental POM [SiMo12O40]-based electrode and more than 3.9 times higher than that of Co-pzta-based electrode. Moreover, at the current density of 10 A g−1, the capacitance retention rate of 1000 cycles of cycle charge and discharge is 86% and 91% respectively. Thus, this work verifies that incorporating POMs with transition-metal complexes is an effective strategy for improving the capacitance performance of pure POMs. Two crystalline coordination hybrids showing intriguing POM-sandwiched porous structures have been synthesized and applied as supercapacitor electrode materials, and it shows high specific capacitance [Display omitted] .