In-plane molecular cord bridging as a method for boosting MXene fiber strength and toughness

MXenes enable high-performance fibers with strength, toughness, and conductivity, yet weak edge-to-edge interactions between nanosheets remain a critical challenge. Inspired by the cord-bound architecture of lamellar armor, we use molecular cords of carboxymethyl cellulose-wrapped single-walled carbon nanotubes to bridge adjacent MXene nanosheets via ionic coordination. Through mild and continuous wet-spinning, crosslinking, and hot-pressing, we fabricate MXene fibers containing only 0.12 wt% of the molecular cords that deliver enhanced mechanical properties: a tensile strength of 1.48 ± 0.06 GPa (peak: 1.55 GPa), ductility of 17.7 ± 0.8%, and toughness of 131.0 ± 8.7 MJ m^-3 (peak: 140 MJ m^-3), representing enhancements of 480%, 300%, and 1620% over pristine MXene fibers, while retaining electrical conductivity above 10,400 S cm^-1 and a volumetric capacitance of 1645 F cm^-3. These molecular cords reinforce interlayer bonding and in-plane bridges, enabling efficient stress transfer and crack inhibition in 2D nanosheet fibers. This molecular cord strategy could potentially be applied to maximize the mechanical performance of fibers derived from other two-dimensional nanosheets.