Water cluster encapsulated polyoxometalate-based hydrogen-bonded supramolecular frameworks (PHSFs) as a new family of high-capacity electrode materials

Water cluster encapsulated polyoxometalate (POM)-based hydrogen-bonded supramolecular frameworks (PHSFs) are novel advanced high-capacity electrode materials for supercapacitors thanks to synergistic effects from internal components as well as the existence of numerous electronic transports and proton conductive pathways formed by hydrogen bond interactions. In this work, three new water cluster encapsulated PHSFs: [Cu2(H2O)4H2(imbta)4](PMo12O40)2·6H2O (1), [Cu (H2O)2H4(pybta)4](PMo12O40)2·2H2O (2) and [Ag2H7(pybta)6(PMo12O40)3]·12H2O (3) as well as one new PHSF: [AgH2(imbta)2](PMo12O40) (4) were hydrothermally synthesized, where the imbta and pybta are 1-imidazol-1-ylmethyl-1H-benzotriazole and 1-pyridin-3-ylmethyl-1H-benzotriazole, respectively. The electrochemical properties of the four compound-based electrodes were estimated by cyclic voltammetry, galvanostatic charge-discharge, electrochemically active surface area, and electrochemical impedance spectroscopy. In particular, due to the unique water-cluster-encapsulated PHSF structure with a large number of O–H⋯O interactions, the 1-based electrode has the highest specific capacitance of 710 F·g−1 at 1 A·g−1 among all the four electrodes, which is superior to that of most POM-based electrodes to date. Furthermore, the 1-based electrode exhibits an excellent capacitance retention about 91.2 % after 1000 cycles at a high charge/discharge current density of 10 A·g−1. The results of this study provide inspiration and guidance for the construction of PHSF-based electrode materials, which have broad application potential in a new-generation of high-performance energy storage devices.