Comparative study on fabrication and energy storage performance of Ti 3 C 2 Tx MXene by using hydrofluoric acid and in situ forming of hydrofluoric acid‐based approaches

Hydrofluoric acid and in situ forming of hydrofluoric acid-based approaches have been experimentally proved to be the effective routes to prepare Ti3C2Tx MXene. Herein, these two approaches are studied. It was found that by using hydrofluoric acid-based approach, Ti3C2Tx MXene with well-defined accordion-like morphology was obtained, while crinkled morphology was observed in the case of in situ forming of hydrofluoric acid etching. The experimental results showed that the specific capacitance decreased with the concentration of hydrofluoric acid because the excessive terminations on the surface of Ti3C2Tx MXenes can block ion transportation. In both approaches, the specific capacitance of the samples increased with the increase in etching time. Li+ can spontaneously intercalate into the Ti3C2Tx layers during the in situ forming of hydrofluoric acid etching of Ti3AlC2, which significantly expanded the lattice space of the resulting Ti3C2Tx. Consequently, in situ forming of hydrofluoric acid etched the samples prevail over the hydrofluoric acid etched ones in electrochemical performance. A different energy storage mechanism was discovered: a capacitive dominant behavior was proved for the 24 hours in situ forming of hydrofluoric acid etched sample, and it showed a specific capacitance of 428.5 F/g, and 98.5% of the specific capacitance was retained after 10 000 cycles of test, while it depends on the scan rate of CV for the hydrofluoric acid etched sample, with only 22.0 F/g and 97.2% of capacitance retention.