MXene films are attractive for advanced supercapacitor electrodes requiring high volumetric energy density due to their high redox capacitance combined with extremely high packing density. However, the self‐restacking of MXene flakes unavoidably decreases the volumetric performance, mass loading, and rate capability. Herein, a simple strategy is developed to prepare a flexible and free‐standing modified MXene/holey graphene film by filtration of the alkalized MXene and holey graphene oxide dispersions, followed by a mild annealing treatment. After terminal groups (—F/—OH) are removed, the increased proportion of Ti atoms enables more pseudocapacitive reaction. Meanwhile, the embedded holey graphene effectively prevents the self‐restacking of MXene and forms a high nanopore connectivity network, which is able to immensely accelerate the ion transport and shorten transport pathways for both ion and electron. When applied as electrode materials for supercapacitors, it can deliver an ultrahigh volumetric capacitance (1445 F cm−3) at 2 mV s−1, excellent rate capability, and high mass loading. In addition, the assembled symmetric supercapacitor demonstrates a fantastic volumetric energy density (38.6 Wh L−1), which is the highest value reported for MXene‐based electrodes in aqueous electrolytes. This work opens a new avenue for the further exploration of MXene materials in energy storage devices.

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MXene films are attractive for use in advanced supercapacitor electrodes on account of their ultrahigh density and pseudocapacitive charge storage mechanism in sulfuric acid. However, the self-restacking of MXene nanosheets severely affects their rate capability and mass loading. Herein, a free-standing and flexible modified nanoporous MXene film is fabricated by incorporating Fe(OH)3 nanoparticles with diameters of 3-5 nm into MXene films and then dissolving the Fe(OH)3 nanoparticles, followed by low calcination at 200 °C, resulting in highly interconnected nanopore channels that promote efficient ion transport without compromising ultrahigh density. As a result, the modified nanoporous MXene film presents an attractive volumetric capacitance (1142 F cm-3 at 0.5 A g-1) and good rate capability (828 F cm-3 at 20 A g-1). Furthermore, it still displays a high volumetric capacitance of 749 F cm-3 and good flexibility even at a high mass loading of 11.2 mg cm-2. Therefore, this flexible and free-standing nanoporous MXene film is a promising electrode material for flexible, portable and compact storage devices. This study provides an efficient material design for flexible energy storage devices possessing high volumetric capacitance and good rate capability even at a high mass loading.

Metal–organic framework (MOF)-derived magnetic metal/carbon nanocomposites have shown tremendous potential for lightweight electromagnetic wave (EMW) absorption. However, it is a challenge but highly significant to design and construct mixed-dimensional hierarchical architectures with synergistically integrated characteristics from individual MOFs for advancing the EMW absorption performance. Inspired by the structure of cactus, a novel hierarchical one-dimensional (1D)–two-dimensional (2D) mixed-dimensional Co/N-decorated carbon architecture comprising carbon nanotubes grafted on carbon flakes (abbreviated as CoNC/CNTs) has been fabricated by the pyrolysis of bimetallic CoZn-ZIF-L. The CoNC/CNTs integrate the advantages of 1D nanotubes for the extra polarization of EMW and 2D nanoflakes with an interconnected porous structure for multiple reflection losses of EMW and optimization of impedance matching. The resultant CoNC/CNTs demonstrate excellent EMW absorbing performance. For the optimal EMW absorbing material of CoNC/CNT-3/1, minimum reflection loss reaches −44.6 dB at 5.20 GHz with a low filler loading of 15 wt %. Moreover, the largest effective bandwidth range achieves 4.5 GHz with a thickness of 1.5 mm and a filled ratio of 20 wt %. These findings indicate that such a mixed 1D–2D hierarchical architecture synergistically enhances EMW absorbing performance. This work sheds light on the rational design of a mixed-dimensional carbon architecture derived from MOFs for desirable functionalities.