Development of polyoxometalate-anchored 3D hybrid hydrogel for high-performance flexible pseudo-solid-state supercapacitor

Abstract

A highly interconnected three-dimensional (3D) networked conductive polypyrrole (PPy) hydrogel anchored with uniformly distributed phosphomolybdic acid (PMo12/PPy hybrid hydrogel) was fabricated by one spot in-situ crosslinking-polymerization strategy. The interconnected 3D hydrogel frameworks not only realize homogenous distributing of PMo12 active particles against aggregation, but also provide continuous transport highways for electron and ion. The specific capacitance of the PMo12/PPy hybrid hydrogel was evaluated in three-electrode system to be 776 F/g, which are almost 2.5 fold higher than that of conventional PMo12/PPy composites. Density functional theory (DFT) calculates the hydrogen bonding strength between cross-linker (TCPP) and PPy to be comparable with the force between closely packed PPy chains. Consequently, the TCPP crosslink with PPy to form a stable 3D porous structure, which provides more adsorb sites for PMo12, bring better stability than conventional PMo12/PPy composites. Meanwhile, the assembled liquid-state device achieves its specific capacitance of 300 F/g and obtains a high rate capability and good cycling stability. The assembled solid-state supercapacitor delivers a maximum specific capacitance of 162.1 F/g, high energy density of 50.66 Wh/kg at power density of 750 W/kg, displays excellent electrochemical performances exceeding those of other polyoxometalate (POM) or metal oxide-based systems to the best of our knowledge. Furthermore, the fabricated supercapacitor was disclosed to render very high capacitance when bended. The fabrication of such a flexible pseudo-solid-state energy storage device is an important breakthrough towards achieving superior performance not possible with conventional polymer/POM composite.