Cyclocrosslinked polyphosphazene modified MXene as aqueous supercapacitor

Abstract

MXenes suffer from severe restacking and oxidative degradation, which may cause the loss of functional properties and hamper further applications in aqueous energy storage devices. It has been proven that MXenes' physical/electrochemical properties are strongly dependent on surface terminations. Establishing the relationship between the molecular configuration, electronic structure of surface modifier and the chemical/electrochemical properties is critical for designing MXene-based aqueous energy storage devices. Herein, a cyclocrosslinked polyphosphazene modified MXene (MXene/PZS) is fabricated by forming the Ti−O−P covalent bond through nucleophilic addition and successive condensation reaction. The MXene/PZS enables faster ion transport, enhanced ion accessibility and stronger oxidation resistance through the combined pillar, steric, and electronic effects provided by the cyclocrosslinked polyphosphazene, leading to pseudocapacitance of 380 F g−1 with superb rate performance. Moreover, the fabricated quasi-solid-state flexible symmetric supercapacitor shows an ultrahigh energy density of 12.26 Wh kg−1 at 0.125 kW kg−1, displaying remarkable flexibility and integrability. Our findings provide a holistic understanding of how the MXenes' physical/electrochemical properties influenced by the surface modifier, thus promoting the design of MXene-based aqueous energy devices.