Surface Engineering of Ti₃C₂T_x MXenes via Silanol Functionalization for Improved Electrochemical Performance

MXenes, a class of 2D transition metal carbides and nitrides, hold immense potential for energy storage applications due to their high electrical conductivity, large specific surface area, and tunable surface chemistry. However, their practical implementation in supercapacitors is hindered by structural instability and limited cycling durability. Here, the covalent functionalization of Ti₃C₂T_x MXenes with 5,5'-bis(triisopropoxysilyl)-2,2'-bipyridine (BPS) to mitigate these limitations is investigated. The functionalization is performed in three different solvents, i.e., m-xylene, ethanol, and isopropanol, to elucidate the influence of solvent choice on surface modification efficacy. X-ray photoelectron spectroscopy confirms BPS incorporation in all samples, but only m-xylene promotes effective functionalization without excessively compromising charge transport. Notably, Ti₃C₂T_x-BPS (m-xylene) shows enhanced ionic conductivity (2.95 mS cm^-1), improved H⁺ diffusion (4.08 × 10^-12 cm² s^-1), and higher pseudocapacitive contributions compared to pristine Ti₃C₂T_x. When used as the negative electrode in an asymmetric supercapacitor, the Ti₃C₂T_x-BPS//activated carbon device achieves a maximum energy density of 32.3 Wh kg^-1 and a power density of 12 300 W kg^-1, with 88.36% capacitance retention after 15 000 cycles, significantly outperforming the pristine Ti₃C₂T_x. These findings highlight the critical role of solvent selection in achieving effective functionalization and demonstrate its impact on the development of robust, high-performance MXene-based supercapacitors.