Novel 2D/2D 1T-MoS₂/Ti₃C₂T heterostructures for high-voltage symmetric supercapacitors

Electrode materials play a crucial role in the electrochemical performance of supercapacitors (SCs). In recent years, 1T-MoS₂ and MXene have been extensively studied as potential electrode materials. However, 1T-MoS₂ suffers from the metastable property, rigorous synthesis process, and nanosheet restacking issue, while the specific capacitance of MXene is restricted, limiting their supercapacitor performance. To fully exploit the advantages of both materials and address their respective problems, 1T-MoS₂/Ti₃C₂T 2D/2D heterostructures are synthesized through a simple hydrothermal method. The existence of heterojunctions is confirmed by XPS and TEM. The different ratios between MoS₂ and Ti₃C₂T are investigated, and the electrochemical test is carried out in a "water-in-salt" electrolyte (20 mol kg^-1 LiCl). The results demonstrate that the heterostructures exhibit enhanced electrochemical performance. The optimized ratio of 1T-MoS₂/Ti₃C₂T is 2 : 1, and the specific capacitance reaches 250 F g^-1 at 1 A g^-1 with a wide potential window of -0.9 to 0.5 V vs. Ag/AgCl. The capacitance retention is 82.3% (at 10 A g^-1) after 5000 cycles, and the average coulombic efficiency (ACE) was 99.96%. Assembled into symmetric SCs (SSCs), the energy density of 12.0 W h kg^-1 at a power density of 139.9 W kg^-1 is achieved with a high voltage of 1.4 V. It also has 82.6% capacitance retention and 99.95% ACE after 5000 cycles at 5 A g^-1. This work is expected to stimulate novel research towards the wide application of 2D/2D heterostructures in SCs.