Ultra Stable Ink with Promising Areal Capacitance as Advanced Micro‐Supercapacitor and Unique Metal Absorptivity Enabled by Surface Functionalization of Titanium Carbide (MXene)

Abstract 2D Ti 3 C 2 T x ‐MXenes have gained attention as highly promising materials owing to their distinctive characteristics. Even so, the limited ionic kinetics and active site exposure of these materials are hindered by the significant degradation caused by oxidation, as well as the challenges in ink formulation processability and nanosheet restacking. Here, this study presents a single‐step and economical method to embellish cysteine onto titanium carbide (MX‐C) nanosheets. Cysteine is found to facilitate the tuning of the interlayer spacing in MXene nanosheets. The idea is then applied in the development of micro‐supercapacitors (MSCs) and the removal of toxic metal ions, specifically lead. In addition, the investigation reveals that MX‐C exhibits antioxidant behavior and possesses excellent qualities as inks. The MX‐C‐printed MSC exhibits ultra‐high areal capacitance (68 mF cm −2 (<N> = 5)) and power density (170.6 µW cm −2 ) compared to the reported printed MSC system. Similarly, the MX‐C facilitates a high capacity for selectively adsorbing lead while also exhibiting excellent performance in terms of adsorption–desorption. The adsorption‐induced effectiveness of cysteine is additionally validated by density functional theory simulations. The versatile approach emphasizes the potential of MX‐C inks with antioxidation properties for the invention of MSCs and metal uptake for printable electronics and clean water applications, respectively.