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

To research the application of polyoxometalates (POMs)-based supramolecular crystalline materials in supercapacitors, two new compounds, (H3PW12O40)-O-VI center dot(BPE)(2.5)center dot 3H(2)O(1) and (H3PMo12O40)-O-VI center dot(BPE)(2.)(5)center dot 3H(2)O (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 ([(H3PW12O40)-O-VI] or [(H3PW12O40)-O-VI] 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 (H3PW12O40)-O-VI, 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.