High supercapacitance performance of nitrogen-doped Ti3C2Tx prepared by molten salt thermal treatment

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Ti3C2Tx with –F surface terminations were treated in LiCl-KCl-Li3N molten salt at atmospheric pressure to introduce N and simultaneously remove –F surface terminations, in which LiCl-KCl salt was used as the solvent and Li3N as the nitrogen source. By optimizing the mass ratio of Li3N:Ti3C2Tx to be 1:2, N-doped Ti3C2Tx (N-Ti3C2Tx-0.5) was obtained with 19.6 at% nitrogen element and 0.69 at% –F surface terminations, leading to the substitution of C by N atoms and the d-spacing expansion from 0.96 to 1.15 nm. Owing to its good electrical conductivity and high electrochemical activity area, the N-Ti3C2Tx-0.5 electrode showed a higher specific capacitance (332 F g−1 at 0.5 A g−1 in 1 M H2SO4 solution), good rate performance (83.1% at 20 A g−1), and excellent capacitance retention (87.5% after 10 000 charging-discharging cycles). This paves a new way to achieve MXene electrodes with high specific capacitances and excellent retention performance.