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, H 3 PW VI 12 O 40 · (BPE) 2.5 · 3H 2 O( 1 ) and H 3 PMo VI 12 O 40 · (BPE) 2.5 · 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 ([H 3 PW VI 12 O 40 ] or [H 3 PMo VI 12 O 40 ]) 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 H 3 PMo VI 12 O 40 , 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. Graphic abstract 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(PW 12 and PMo 12 ). 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).