Electrochemical Capacitance of CNF-TiCT MXene-Based Composite Cryogels in Different Electrolyte Solutions for an Eco-Friendly Supercapacitor.

Cellulose nanofibrils (CNFs) are promising materials for flexible and green supercapacitor electrodes, while TiCT MXene exhibits high specific capacitance. However, the diffusion limitation of ions and chemical instability in the generally used highly basic (KOH, MXene oxidation) or acidic (HSO, CNF degradation) electrolytes limits their performance and durability. Herein, freestanding CNF/MXene cryogel membranes were prepared by deep freeze-casting (at -50 and -80 °C), using different weight percentages of components (10, 50, 90), and evaluated for their structural and physico-chemical stability in other less aggressive aqueous electrolyte solutions (Na/Mg/Mn/K-SO, NaCO), to examine the influence of the ions transport on their pseudocapacitive properties. While the membrane prepared with 50 wt% (2.5 mg/cm) of MXene loading at -80 °C shrank in a basic NaCO electrolyte, the capacitance was performed via the forming of an electroactive layer on its interface, giving it high stability (90% after 3 days of cycling) but lower capacitance (8 F/g at 2 mV/s) than in HSO (25 F/g). On the contrary, slightly acidic electrolytes extended the cations' transport path due to excessive but still size-limited diffusion of the hydrated ions (SO > Na > Mn > Mg) during membrane swelling, which blocked it, reducing the electroactive surface area and lowering conductivities (<3 F/g).