Effect of temperature and atmosphere on V2AlC etching for V2CTxMXenes synthesis used as anode for Li-ion storage systems

This study investigated the effect of the Ar-controlled atmosphere on the etching of the V2AlC MAX phase and the electrochemical properties for Li-ion storage. First, the V2AlC MAX phase was etched at room temperature for 92 h by 48 % HF acid in an ambient atmosphere. The results showed incomplete etching, and HF's penetration paths into the MAX phase were closed due to oxidation. Second, the etching process was conducted in an Ar- controlled atmosphere. The process was done in different temperatures, 9, 25, and 40 °C. The EDS results showed that an increase in temperature is necessary for completing the etch reaction. Also, controlling the temperature (9 °C) during the MAX phase addition to the acid prevents an oxide layer on the MAX phase surface. Therefore, the paths for the penetration of the acid into the V2AlC MAX phase will remain open, and the etching process by increasing the temperature up to 40 °C will be more progressed. The discharge capacity of Li-ion storage for the V2CTx,which was etched at 9 + 40 °C in an Ar-controlled atmosphere for 92 h by 48 % HF acid, was 500.5 mAh g−1at 50mA g−1for the first cycle and 388.5 mAh g−1at 100mA g−1after 100cycles with 99.4 % coulombic efficiency.