Free-Standing MXene/Carbon Nanotube@Fe₂O₃ Film Electrodes with High Capacitance for All-in-One Supercapacitors

As a critical power source, thin film supercapacitors are highly desirable for constructing flexible electronics due to their tiny volume, flake morphology, and shape deformability. However, they suffer from low energy storage capacity and a tedious fabrication process caused by the limitations of conventional electrode and device structures. Through a layer-by-layer assembly strategy using the vacuum-filtration technique, a MXene-based composite film electrode and an all-in-one structured device are developed in the present study. Tuning the stacked layer structure of MXene films with the carbon nanotube@Fe 2 O 3 (CNT@Fe 2 O 3 ) composites achieves a large accessible active surface area, efficient ion diffusion channels, and additional pseudocapacitance of Fe 2 O 3 without significantly affecting the weight, volume, and thickness of electrodes. Moreover, the dual conductive network that is constructed by MXene nanosheets and CNTs avoids the negative influence of Fe 2 O 3 on the conductivity and stability of whole electrodes. Benefiting from the unique electrode structure, the obtained MXene/CNT@Fe 2 O 3 film electrode shows high capacity (487.5 F g –1, 468.8 F cm –3, 1.969 F cm –2 ), good cycling stability, and structural flexibility. The assembled all-in-one film supercapacitor also shows a high volumetric energy density of 5.3 mWh cm –3 and great potential in practical application.