Free-Standing MXene/Carbon\nNanotube@Fe<sub>2</sub>O<sub>3</sub> Film Electrodes with High Capacitance\nfor All-in-One\nSupercapacitors

As a critical power source, thin film supercapacitors\nare highly\ndesirable for constructing flexible electronics due to their tiny\nvolume, flake morphology, and shape deformability. However, they suffer\nfrom low energy storage capacity and a tedious fabrication process\ncaused by the limitations of conventional electrode and device structures.\nThrough a layer-by-layer assembly strategy using the vacuum-filtration\ntechnique, a MXene-based composite film electrode and an all-in-one\nstructured device are developed in the present study. Tuning the stacked\nlayer structure of MXene films with the carbon nanotube@Fe<sub>2</sub>O<sub>3</sub> (CNT@Fe<sub>2</sub>O<sub>3</sub>) composites achieves\na large accessible active surface area, efficient ion diffusion channels,\nand additional pseudocapacitance of Fe<sub>2</sub>O<sub>3</sub> without\nsignificantly affecting the weight, volume, and thickness of electrodes.\nMoreover, the dual conductive network that is constructed by MXene\nnanosheets and CNTs avoids the negative influence of Fe<sub>2</sub>O<sub>3</sub> on the conductivity and stability of whole electrodes.\nBenefiting from the unique electrode structure, the obtained MXene/CNT@Fe<sub>2</sub>O<sub>3</sub> film electrode shows high capacity (487.5 F\ng<sup>–1</sup>, 468.8 F cm<sup>–3</sup>, 1.969 F cm<sup>–2</sup>), good cycling stability, and structural flexibility.\nThe assembled all-in-one film supercapacitor also shows a high volumetric\nenergy density of 5.3 mWh cm<sup>–3</sup> and great potential\nin practical application.