Synthesis of Mo₂C 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-, etc.), 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 degrees C for 24 h. After intercalation by hexadecyl trimethyl ammonium bromide at 90 degrees 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 center dot g(-1) at 0.8 A center dot g(-1), which is 52% higher than that Mo2C made by HF etching (175.77 mAh center dot 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.