Effect of Postetch Annealing Gas Composition on the Structural and Electrochemical Properties of Ti 2 CT x MXene Electrodes for Supercapacitor Applications

Two-dimensional Ti 2 CT x MXene nanosheets were prepared by the selective etching of Al layer from Ti 2 AlC MAX phase using HF treatment. The MXene sheets retained the hexagonal symmetry of the parent Ti 2 AlC MAX phase. Effect of the postetch annealing ambient (Ar, N 2, N 2 /H 2, and air) on the structure and electrochemical properties of the MXene nanosheets was investigated in detail. After annealing in air, the MXene sheets exhibited variations in structure, morphology, and electrochemical properties as compared to HF treated MAX phase. In contrast, samples annealed in Ar, N 2, and N 2 /H 2 ambient retained their original morphology. However, a significant improvement in the supercapacitor performance is observed upon heat treatment in Ar, N 2, and N 2 /H 2 ambients. When used in symmetric two-electrode configuration, the MXene sample annealed in N 2 /H 2 atmosphere exhibited the best capacitive performance with specific capacitance value (51 F/g at 1A/g) and high rate performance (86%). This improvement in the electrochemical performance of annealed samples is attributed to highest carbon content, and lowest fluorine content on the surface of the sample upon annealing, while retaining the original two-dimensional layered morphology and providing maximum access of aqueous electrolyte to the electrodes.