High-performance flexible supercapacitor enabled by Polypyrrole-coated NiCoP@CNT electrode for wearable devices

The flexible ASC device with NCP@CNT10@PPy6 as the cathode and AC as the anode shows excellent electrochemical performance and great application potentials in heat-resistant storage energy systems and portable wearable devices. • DFT calculation confirms the combination of Ni and Co is conducive to rapid electron transfer. • Carboxylic carbon nanotubes are used to load nickel-cobalt bimetallic phosphide, and polypyrrole is further coated on the surface to accelerate electron transfer and maintain a stable structure. • The NCP@CNT10@PPy6 delivers high specific capacitance, high rate performance and excellent cycle stability. • A flexible supercapacitor device is synthesized based on NCP@CNT10@PPy6 and possesses a stable working state under a wide range of operating temperatures and bending angles. As a pseudocapacitive electrode material, nickel–cobalt bimetallic phosphide has attracted wide attention with its advantage in capacitance and chemical activity. While, like Ni-Co oxides or sulfides, the application of nickel–cobalt bimetallic phosphide is generally hampered by its confined conductivity, low chemical stability and unsatisfactory cycle durability. Herein, this work demonstrates a NiCoP@CNT@PPy (NCP@CNT@PPy) composite that is obtained by polymerizing pyrrole monomer on the surface of NiCoP@CNT complex. According to density functional theory (DFT), it is theoretically demonstrated that the bimetallic Ni-Co phosphide (NiCoP) can exhibit more electrons near the Fermi level than single Ni or Co phosphide. Under the combined effects of carboxylic carbon nanotubes (c-CNTs) and polypyrrole (PPy), the NCP@CNT@PPy electrode exhibits excellent electrochemical performance. In addition, a flexible asymmetric supercapacitor (ASC) is prepared, which demonstrated high energy density and admirable heat-resistance and flexibility performance, showing huge potential in the application of heat-resistant storage energy systems and portable wearable devices.