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

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.