Three-dimensional supramolecular crystalline materials based on Keggin-based polyoxometalates and 1,2-Bis (4-pyridyl) ethylene for supercapacitor electrodes

Abstract

To research the application of polyoxometalates (POMs)-based supramolecular crystalline materials in supercapacitors, two new compounds, H3PWVI12O40·(BPE)2.5·3H2O(1) and H3PMoVI12O40·(BPE)2.5·3H2O (2) (BPE = 1,2-Bis(4-pyridyl)ethylene) have been synthesized by a one-step hydrothermal method. Their structures are determined by single-crystal X-ray diffraction analysis and further characterized by FTIR spectroscopy, powder X-ray diffraction, and bond valence sum analysis. The POMs cluster ([H3PWVI12O40] or [H3PMoVI12O40]) acts as a connector to connect five BPE units through hydrogen bonds, generating a three-dimensional structure. The capacitance performance of these two compounds is tested by cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy. Compared with compound 1 and parent H3PMoVI12O40, compound 2 shows better electrochemical performances with a capacitance of 137.5 F g–1 at 2 A g–1. Compound 2 also has good cycle stability at a current density of 10 A g–1 and still has an initial capacitance of 92% after 1000 cycles. This work shows that hybrid supramolecular crystal materials based on polyoxometalates may provide an alternative way to improve the performance of POMs-based capacitor electrode materials. Two POMs-based supramolecular crystalline materials were synthesized by a hydrothermal method. The supercapacitor performance of these two compounds is better than their parents POMs(PW12 and PMo12). Among them, compound 2 displays specific capacitance (137.5 F g–1 at 2 A g–1) and better cycle stability (92.0% after 1000 cycles).