Flexible and hollow polypyrrole foam with high loading of metal–organic framework nanowires for wearable supercapacitors

Abstract

Metal–organic frameworks (MOFs) with intramolecular pores have been widely explored as promising active materials in supercapacitor electrodes. Nevertheless, low conductivity of general MOFs is the major bottleneck hindering their capacitance. In this study, a facile strategy has been designed to construct a three-dimensional hybrid architecture of flexible polypyrrole hollow foam with high loading of conductive Ni-CAT MOF nanowires (PPy HF/Ni-CAT-NWs) as a self-standing electrode free of any substrates, conductive agents and binders. The PPy foam with hollow skeletons provides high surface area and efficient conductive networks as well as inherent capacitance, acting as a flexible matrix in the electrode. The Ni-CAT-NWs are deposited onto both the exterior and interior surfaces of PPy foam skeletons to achieve high MOF loading, which could afford decent conductivity and high porosity for enhanced electron/ion accessibility. The PPy HF/Ni-CAT-NW electrode exhibits a satisfactory areal capacitance of over 1050 mF cm⁻² (at 0.5 mA cm⁻²). The assembled symmetric solid-state supercapacitor demonstrates superior electrochemical energy-storage properties as well as excellent mechanical flexibility and working temperature tolerance, and could be fabricated into a wearable wristband to drive an electronic watch, displaying strong potential for wearable electronics. This study provides some valuable insights into MOF-based composite electrodes for wearable energy-storage devices.