Synthesis of Mo ₂C MXene with high electrochemical performance by alkali hydrothermal etching

Two-dimensional MXenes are generally prepared by the etching of acid solutions. The as-synthesized MXenes are terminated by acid group anions (F^–, Cl^–, et al.), which affect the electrochemical performance of MXenes. Here, we report a novel method to prepare Mo₂C MXene from Mo₂Ga₂C by the hydrothermal etching of alkali solutions. Highly pure Mo₂C MXene was successfully synthesized by the etching of NaOH, while the etchings of LiOH and KOH were failed. The concentration of NaOH, temperature and time strongly affect the purity of as-prepared MXene. Pure Mo₂C MXene could be synthesized by the etching of 20 M NaOH at 180 °C for 24 h. After intercalation by hexadecyl trimethyl ammonium bromide at 90 °C for 96 h, few-layer Mo₂C MXene was obtained. The Mo₂C MXene made by NaOH etching after intercalation exhibited excellent performance as anode of lithium-ion battery, compared with general Mo₂C MXene made by HF etching and the Mo₂C MXene reported in literature. The final discharge specific capacity was 266.73 mAh·g^-1 at 0.8 A·g^-1, which is 52% higher than that Mo₂C made by HF etching (175.77 mAh·g^-1). This is because Mo₂C MXene made by NaOH etching has lager specific surface area, lower resistance, and pure O/OH termination without acid anion termination. This is the first report to make Mo₂C MXene by alkali etching and the samples made by this method exhibited significantly better electrochemical performance than the samples made by general HF etching.