Hao Peng, Yanan Zhang, Dong Li, Hongxing Chen, Fengxia Geng
Ti 3 C 2 T x holds great promise as an electrode material for high-capacitance supercapacitors, owing to its large specific surface area, pseudocapacitive behavior, and excellent electrical conductivity. However, the commonly used MILD synthesis method based on HCl/LiF etching introduces electrochemically inert −F terminations, which hinder ion storage and make the surface prone to oxidation. In this work, we report a modified MILD etching protocol using a significantly reduced LiF concentration under hydrothermal conditions at elevated temperatures. The lower LiF concentration and the higher etching temperature promote the formation of −O and minimize −F surface terminations. The resulting Ti 3 C 2 film exhibits far fewer −F terminations than conventional films (Ti 3 C 2 –O 1.37 (OH) 0.35 F 0.36 ·0.35H 2 O vs Ti 3 C 2 –O 0.96 (OH) 0.39 F 0.75 ·0.47H 2 O). The oxygen-rich Ti 3 C 2 film allows for enhanced proton-coupled electron transfer and reversible redox reactions in H 2 SO 4, thus delivering a gravimetric capacitance of 511 F g –1 at 1 A g –1, 1.61 times higher than its counterpart obtained by conventional MILD method. The film retains 93.6% capacitance at 20 A g –1 and shows no performance degradation over 10,000 cycles. When assembled in asymmetric configuration with activated carbon, the device achieves a maximum energy density of 25.0 Wh kg –1 at 375 W kg –1 and maintains 15.4 Wh kg –1 at a high power density of 15,000 W kg –1 . Devices with gel electrolyte also show good performance under practical conditions, including in parallel and series configurations as well as under bending deformation. This study presents a scalable strategy to tailor MXene surface chemistry for high-energy, high-power energy storage applications.