Fe2O3 Nanoparticles Anchored on the Ti3C2Tx MXene Paper for Flexible Supercapacitors with Ultrahigh Volumetric Capacitance

Ti3C2Tx MXene, with high conductivity and flexibility, has drawn great attention in the wearable energy storage devices. However, the easy nanoflake-restacking phenomenon greatly restricts the achievable electrochemical performance of Ti3C2Tx-based supercapacitors, in particular volumetric capacitance. Herein, we report a flexible hybrid paper consisting of Fe2O3 nanoparticles (NPs) anchored on Ti3C2Tx (Fe2O3 NPs@MX) via electrostatic self-assembly and annealing treatments. The interlayer spacing of Ti3C2Tx nanoflakes is effectively enlarged through the incorporation of Fe2O3 NPs, allowing more electrochemical active sites to store charge. Meanwhile, Ti3C2Tx nanoflakes form a continuous metallic skeleton and inhibit the volume expansion of Fe2O3 NPs during the charging/discharging process, enhancing the cycling stability. The flexible, ultrathin (4.1 μm) Fe2O3 NPs@MX hybrid paper shows considerably improved electrochemical performances compared to those of pure Ti3C2Tx and Fe2O3, including a wide potential window of 1 V, an ultrahigh volumetric capacitance of ∼2607 F cm-3 (584 F g-1), and excellent capacitance retention after 13,000 cycles. Besides, the as-assembled symmetric solid-state supercapacitor exhibits an energy density of 29.7 Wh L-1 and excellent mechanical flexibility. We believe that the present nanostructure design, decorating NPs within a two-dimensional metallic network, has general applicability and could be used to fabricate highly efficient composites for advanced energy storage devices.