Nitrogen-doped Ti 3 C 2 T x MXene electrodes for high-performance supercapacitors

A new type of nitrogen-doped two-dimensional MXene (N-Ti3C2Tx) was synthesized by post-etch annealing Ti3C2Tx in ammonia as a promising electrode material for supercapacitors. The concentrations of nitrogen can be rationally controlled to produce N-Ti3C2Tx materials with 1.7–20.7 at% of nitrogen by simply tuning the annealing temperatures from 200 °C to 700 °C. The introduction of nitrogen as a heteroatom in the Ti3C2Tx structure leads to a remarkable increase of the c-lattice parameter of MXene sheets from 1.92 nm in Ti3C2Tx to 2.46 nm in N-doped ones upon ammonia treatment at 200 °C. More interestingly, the resultant doped MXene materials under optimized condition exhibited drastically improved electrochemical capacitances of 192 F g−1 in 1 M H2SO4 and 82 F g−1 in 1 M MgSO4 electrolyte, which are remarkably higher than those of the un-doped Ti3C2Tx materials (34 F g−1 in 1 M H2SO4 and 52 F g−1 in 1 M MgSO4).