Stable carbon encapsulated titanium carbide MXene aqueous ink for fabricating high-performance supercapacitors

Ti-based MXenes have shown great promise in electrochemical applications, including (photo)electrocatalysis and energy storage. However, their practical application has been hindered by their rapid oxidation in the presence of water and O₂. In this work, we propose a method to solve the problem through a one-step hydrothermal treatment of MXene (Ti₃C₂T_x, where T_x is –OH or –F) in the presence of agarose. The hydrothermal treatment results in the in situ capping of the phenolic carbon layer on the Ti₃C₂T_x to form Ti₃C₂T_x@C, which improves its chemical stability by protecting the Ti atoms from oxidation with water and O₂, and thus enhances its electrochemical performance by avoiding re-stacking of the Ti₃C₂T_x@C sheets. The as-prepared Ti₃C₂T_x@C exhibits high oxidation resistance with >95% performance when stored in an aqueous medium for at least 100 days. Ti₃C₂T_x@C provides a specific capacitance of 736 F g^–1 in 1 M H₂SO₄ electrolyte over a voltage window of 0.5 V. Having excellent water dispersibility and high electrochemical activity, Ti₃C₂T_x@C is ideal for the preparation of stable MXene inks for the fabrication of high-performance interdigitated electrodes through inkjet printing. The flexible micro-supercapacitor constructed from Ti₃C₂T_x@C ink exhibits excellent cyclic stability up to 10,000 charge-discharge cycles without a significant decrease in specific capacitance.