Wrinkled two-dimensional ultrathin Cu(ii)-porphyrin framework nanosheets hybridized with polypyrrole for flexible all-solid-state supercapacitors

Abstract

Two-dimensional (2D) metal porphyrin frameworks (MPFs) with a π-conjugated skeleton, high surface area, and more accessible active sites have been applied as active materials for supercapacitors, but the poor electrical conductivity limits the enhancement of electrochemical performance. Moreover, MPF-based flexible supercapacitors have been rarely reported. Here, for the first time, we fabricated wrinkled 2D ultrathin 5,10,15,20-tetrakis(4-carboxylphenyl)porphyrin copper(II) (Cu-TCPP) nanosheets through the surfactant-assisted synthetic method. The as-obtained wrinkled Cu-TCPP nanosheets were further composited with conductive polypyrrole (PPy) to construct a flexible Cu-TCPP/PPy film through the combination of the electrophoretic deposition method and electrochemical polymerization technology. The wrinkled 2D ultrathin Cu-TCPP nanosheets not only offer macroporous channels for fast ion/electron transport, but also effectively reduce the transmission path of electrolyte ions. The PPy affords 3D conductive networks for rapid electron transport and enhances the electrochemical kinetics. The synergistic effect of Cu-TCPP and PPy leads to the enhanced supercapacitive performance of Cu-TCPP/PPy in comparison with the individual components. As a result, the freestanding Cu-TCPP/PPy electrode shows a capacitance of 340.6 mF cm⁻² at 1 mA cm⁻², 71.14 F cm⁻³ at 0.1 A cm⁻³, and 163.34 F g⁻¹ at 0.2 A g⁻¹, more than 45% greater than that of the pristine PPy film of 224.6 mF cm⁻², 48.15 F cm⁻³ and 92.2 F g⁻¹ at the corresponding current densities. Moreover, the fabricated binder-free symmetric supercapacitor possesses a maximum energy density of 2.27 μW h cm⁻² at the highest power density of 50 μW cm⁻². This work provides a new strategy to design 2D metal–organic framework-based flexible all-solid-state supercapacitors with high energy storage performances.