Enhanced tensile and electrochemical performance of MXene/CNT hierarchical film.

Nowadays, it is highly desirable to achieve high strength, flexibility and electrochemical performance for supercapacitor electrodes simultaneously. Herein, few-layer MXene flakes are assembled into free-standing films by facile vacuum-filtration method, in which hydrophilic-functionalized carbon nanotubes (CNTs) are further incorporated. The morphology of MXene/CNT composite films evolves from compact to 'CNT in MXene' to laminar to 'MXene in CNT' and finally to separate structures when increasing the CNT weight percentage. Among them, the laminar structure in which thin MXene and CNT layers are stacked alternately is demonstrated to be the best. The laminar MXene/CNT film possesses much higher strength, elongation and specific capacitance than MXene film due to the engineered porosity, good interaction between MXene flakes and CNTs, and proper CNTs' distribution. As a result, high specific capacitance of 423.4 F g-1at 1 A g-1and capacitance retention of nearly 60% at 10 A g-1are accomplished. Moreover, the composite film is flexible and withstands bending up to 180°, indicating that the proposed laminar MXene/CNT composite film is a superb candidate for flexible supercapacitors.