A hydrofluoric acid-free synthesis of 2D vanadium carbide (V₂C) MXene for supercapacitor electrodes

Although theoretical calculations predict vanadium carbide (V2C) MXene may possess superior performances as electrodes of supercapacitors and lithium-ion batteries, a milder synthesis process of high-purity V2C MXene undoubtedly becomes one of the greatest hindrances for extending its applications. Herein, we report a hydrofluoric acid (HF)-free synthesis of 2D V2C MXene by milder etching V2AlC powders in the mixture of lithium fluoride and hydrochloric acid. The etching time plays vital roles on the structure and morphology of V2C MXene. The as-synthesized V2C MXene etched for 120 h displays a uniform multilayered structure and higher purity (>90%). All that matter is it exhibits a maximum specific capacitance of 164 F g−1 at a scan rate of 2 mV s−1, good cycling stability and high specific capacitance retention (~90% after 10 000 cycles at 5 A g−1) in 1 M Na2SO4 electrolyte. Moreover, other fluorides, including potassium fluoride, sodium fluoride and ammonium hydrogen fluoride, are also testified to be effective to obtain highly pure V2C MXene. This work provides the certainty for synthesizing MXenes besides Ti3C2 via a HF-free etching process to beneficially expand their promising application.