Flexible supercapacitors (FSCs) are limited in flexible electronics applications due to their low energy density. Therefore, developing electrode materials with high energy density, high electrochemical activity, and remarkable flexibility is challenging. Herein, we designed nitrogen-doped porous MXene (N-MXene), using melamine-formaldehyde (MF) microspheres as a template and nitrogen source. We combined it with an electrospinning process to produce a highly flexible nitrogen-doped porous MXene nanofiber (N-MXene-F) as a self-supporting electrode material and assembled it into a symmetrical supercapacitor (SSC). On the one hand, the interconnected mesh structure allows the electrolyte to penetrate the porous network to fully infiltrate the material surface, shortening the ion transport channels; on the other hand, the uniform nitrogen doping enhances the pseudocapacitive performance. As a result, the as-assembled SSC exhibited excellent electrochemical performance and excellent long-term durability, achieving an energy density of 12.78 Wh kg⁻¹ at a power density of 1080 W kg⁻¹, with long-term cycling stability up to 5000 cycles. This work demonstrates the impact of structural design and atomic doping on the electrochemical performance of MXene and opens up an exciting possibility for the fabrication of highly FSCs.

Sodium-ion batteries (SIBs) are a promising electrochemical energy storage system but face great challenges in developing fast-charging anodes. MXene-based composites are a new class of two-dimensional materials that are expected to be widely used in SIB energy storage due to their excellent electrical conductivity and stable structure. However, MXenes tend to experience interlayer stacking during preparation, which can result in poor electrochemical performance and a lower actual capacity compared to the theoretical value. In this study, the porous structure was created using a chemical oxidation method from a microscopic perspective. The porous MXene (referred to as PM) was prepared by using a low concentration of hydrogen peroxide as the pore-forming solution, which enlarged the interlayer spacing to facilitate the transport of sodium ions in the electrolyte solution. The PM with the addition of hydrogen peroxide solution achieved high-rate performance, with a capacity of 247 mAh g⁻¹ at 0.1 A g⁻¹ and 114 mAh g⁻¹ at 10 A g⁻¹. It also demonstrated long-cycle stability, with a capacity of 117 mAh g⁻¹ maintained over 1000 cycles at 5 A g⁻¹.