Boosting Zn-Ion Storage Behavior of Pre-Intercalated MXene with Black Phosphorus toward Self-Powered Systems

MXene-based Zn-ion capacitors (ZICs) with adsorption-type and battery-type electrodes demonstrate high energy storage and anti-self-discharge capabilities, potentially being paired with triboelectric nanogenerators (TENGs) to construct self-powered systems. Nevertheless, inadequate interlayer spacing, deficient active sites, and compact self-restacking of MXene flakes pose hurdles for MXene-based ZICs, limiting their applications. Herein, black phosphorus (BP)-Zn-MXene hybrid is formulated for MXene-based ZIC via a two-step molecular engineering strategy of Zn-ion pre-intercalation and BP nanosheet assembly. Zn ions as intercalators induce cross-linking of MXene flakes with expandable interlayer spacing to serve as scaffolds for BP nanosheets, thereby providing sufficient accessible active sites and efficient migration routes for enhanced Zn-ion storage. The density functional theory calculations affirm that zinc adsorption and diffusion kinetics are significantly improved in the hybrid. A wearable ZIC with the hybrid delivers a competitive areal energy of 426.3 µWh cm^-2 and ultra-low self-discharge rate of 7.0 mV h^-1, achieving remarkable electrochemical matching with TENGs in terms of low energy loss, matched capacity, and fast Zn-ion storage. The resultant self-powered system efficiently collects and stores energy from human motion to power microelectronics. This work advances the Zn-ion storage of MXene-based ZICs and their synergy with TENG in self-powered systems.