To stabilize the layer structures of MXenes, carbon nanotubes (CNTs) have been successfully grown in situ by a facile microwave irradiation method under ambient conditions. The synthesized composites based on various MXenes including Ti₃C₂, Ti₂C and V₂C exhibited hybrid structures with uniformly distributed multi-walled CNTs anchored on the layer structured MXene networks. Benefiting from the unique structural features, these composites exhibit excellent electrochemical properties as anode materials in lithium ion batteries. The CNTs@Ti₃C₂ composite exhibits high reversible capacities of 430 mA h g⁻¹ at 1 A g⁻¹ and 175 mA h g⁻¹ at 10 A g⁻¹ (31.25 C), and is not only better than the pristine Ti₃C₂ (99 mA h g⁻¹ and 45 mA h g⁻¹, respectively), but also superior to the recently reported MXene composites. The impressive electrochemical performance is attributed to the synergetic effects of the connective CNT bridges, large-capacity metal/metal oxides and the fine conductive MXene matrix. This in situ growth strategy of CNTs shows great potential in modulating the structure and properties of nanomaterials for advanced applications.

Electrically conductive hydrogels are polymeric composites that combine electroactive fillers with hydrogel networks. They offer an electrically conductive pathway for electron transfer and provide an interconnected framework for ion diffusion, as well as an extended active interface for redox reactions, being ideal frameworks to design and construct flexible electrodes. In this work, we integrate nanoscale building blocks into a unique ternary (1, 2 and 3 dimensional) hydrogel architecture, where conductive polymer polypyrrole (PPy) nanofibers (1D) and MXene nanosheets (2D) are uniformly dispersed in polyvinyl alcohol (PVA) matrixes (3D). 1D nanofibers and 2D nanosheets were found to greatly increase the mechanical properties of the hydrogel hosts, demonstrating a remarkable tensile strength of 10.3 MPa and a large elongation over 380%. Moreover, the as-fabricated hierarchical structure effectively promotes electrolyte diffusion, exhibiting exceptional capacitive characteristics, including a high gravimetric specific capacitance of 614 F g⁻¹ (at 1 A g⁻¹) and an unprecedented cycling stability (100% capacitance retention over 10 000 cycles). A solid-state supercapacitor is assembled based on these MXene/PPy-PVA hydrogels, which demonstrates an efficient approach to the fabrication of wearable energy storage devices.