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

Abstract Although theoretical calculations predict vanadium carbide (V 2 C) MXene may possess superior performances as electrodes of supercapacitors and lithium-ion batteries, a milder synthesis process of high-purity V 2 C MXene undoubtedly becomes one of the greatest hindrances for extending its applications. Herein, we report a hydrofluoric acid (HF)-free synthesis of 2D V 2 C MXene by milder etching V 2 AlC powders in the mixture of lithium fluoride and hydrochloric acid. The etching time plays vital roles on the structure and morphology of V 2 C MXene. The as-synthesized V 2 C 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 Na 2 SO 4 electrolyte. Moreover, other fluorides, including potassium fluoride, sodium fluoride and ammonium hydrogen fluoride, are also testified to be effective to obtain highly pure V 2 C MXene. This work provides the certainty for synthesizing MXenes besides Ti 3 C 2 via a HF-free etching process to beneficially expand their promising application.