Rapid advancement of modern electronic devices necessitates the development of materials that can simultaneously provide efficient energy storage and effective microwave absorption. Herein, a novel composite material was prepared via the self-assembly of Fe₃O₄ nanoparticles on the surface of V₂C MXene. This composite exhibited characteristics suitable for supercapacitor and electromagnetic absorption applications, highlighting the synergistic relationship between energy storage and electromagnetic wave absorption capability. The electrochemical tests revealed that the specific capacity of the V₂C MXene/Fe₃O₄ composite (42.67 mAh g⁻¹) considerably improved compared with those of the raw materials. The prepared V₂C MXene/Fe₃O₄//V₂C MXene/Fe₃O₄ symmetric supercapacitor demonstrated an energy density of 44.8 Wh L⁻¹, a power density of 959.4 W L⁻¹ and a capacity retention of 80.14% after 8000 cycles. Moreover, the V₂C MXene/Fe₃O₄ composite exhibited an optimal reflection loss of −42.4 dB in the Ku band, with an effective absorption bandwidth of 1.9 GHz (14.6–16.5 GHz). This composite material exhibits broad application potential in modern electronic devices owing to its high energy storage capacity and effective electromagnetic wave absorption. This dual functionality improves device performance and offers a compact solution for energy storage and effective microwave absorption.

The effect of etching environment (opened or closed) on the synthesis and electrochemical properties of V₂C MXene was studied. V₂C MXene samples were synthesized by selectively etching of V₂AlC at 90 ℃ in two different environments: opened environment (OE) in oil bath pans under atmosphere pressure and closed environment (CE) in hydrothermal reaction kettles under higher pressures. In OE, only NaF (sodium fluoride) + HCl (hydrochloric acid) etching solution can be used to synthesize highly pure V₂C MXene. However, in CE, both LiF (lithium fluoride) + HCl and NaF+HCl etchant can be used to prepare V₂C MXene. Moreover, the V₂C MXene samples made in CE had higher purity and better-layered structure than those made in OE. Although the purity of V₂C obtained by LiF+HCl is lower than that of V₂C obtained using NaF+HCl, it shows better electrochemical performance as anodes of lithium-ion batteries (LIBs). Therefore, etching in CE is a better method for preparing highly pure V₂C MXene, which provides a reference for expanding the synthesis methods of V₂C with better electrochemical properties.