Synergistic interfacial engineering of sandwich-structured polypyrrole@MXene composite films for high-performance flexible all-solid-state supercapacitors

The restacking of MXene nanosheets and the intrinsic instability of conductive polymers severely impede their practical deployment in flexible supercapacitors. Herein, a sandwich-structured polypyrrole@MXene (PPy@MXene) composite film was fabricated via a facile two-step in situ oxidative polymerization strategy. The optimized PPy@MXene-3 electrode exhibits significantly enlarged interlayer spacing, abundant redox-active sites, and a continuous conductive network. Electrochemical analysis reveals a high capacitive contribution of 83.9% at 30 mV s −1 , reflecting surface-dominated kinetics. The electrode delivers superior specific capacitance, low charge-transfer resistance, and outstanding cycling stability, retaining 90.1% of its initial capacitance after 10,000 cycles. Density functional theory (DFT) calculations demonstrate interfacial electron transfer from PPy to MXene, which elevates the density of states at the Fermi level and lowers the H + diffusion barrier (1.36 eV vs. 1.47 eV for pristine MXene). A flexible all-solid-state symmetric supercapacitor assembled with PPy@MXene-3 achieves an energy density of 34.7 Wh kg −1 at a power density of 350 W kg −1 , retains 75.9% of its initial capacitance after 10,000 cycles, and maintains stable performance under various bending angles. This work synergistically integrates conductive polymers with two-dimensional MXene frameworks, establishing a rational electrode design strategy for high-performance, flexible energy-storage devices.