Fig. 2. Characterization of the knotted CNTs and MXene-knotted CNT composite electrodes.

a SEM and b TEM images of the knotted CNTs. c Top view and d cross-sectional SEM images of an MXene-knotted CNT composite electrode with 17% CNTs. e SEM image and f corresponding schematic of how the alignment of the Ti₃C₂ flakes was broken by the knotted CNTs to form 3D networked structure. “a” and “b” (~1:2 ratio) in the schematic correspond to the radius of the knots (taking the knots as circles) and the size of the Ti₃C₂ flakes, respectively. g Cross-sectional SEM images of MXene-knotted CNT composite electrodes with different CNT contents from 0% (pure Ti₃C₂ film) to 34%. Scale bars, 100 nm (a, b), 1 μm (c, g), 2 μm (d), 200 nm (e).