Nano-/Micro-fiber Engineering of Vinylene-Linked Polymeric Frameworks for Flexible Free-Standing Thermoelectric Films

Polymer-based thermoelectric (TE) films feature several prominent merits, involving available multi-component compositions, versatile patterning fabrication, and readily integration. Therefore, these materials hold a huge potential as the continuous power supply for wearable devices. Herein, we reported the preparation of a series of vinylene-linked triazole-cored covalent organic frameworks (COFs) by Knoevenagel condensation of 2, 4, 6-trimethyl-1, 3, 5-triazine as the core monomer. The as-prepared COFs tend to generate the nano- or micro-fiber morphologies with tunable lengths and diameters through changing the polyphenylene building blocks. Accordingly, these COF fibers could be readily composited with single-walled carbon nanotubes (SWCNTs) to form the flexible free-standing films upon a simple vacuum filtration method. A film sample containing 30 wt% g-C₁₈N₃-COF exhibited the highest power factor of 68.93 μW/(m K²) at 420 K. The manipulated 4-leg flexible thermoelectric generator (f-TEG) released a maximum output power and power density of 343.5 nW and 0.32 W/m² at a temperature difference of 35 K. After bending for 1000 times at a radius of 15 mm, the resistance change rate of the as-fabricated f-TEGs was less than 5%, exhibiting excellent stability and flexibility. This work might not only broaden the potential application scope of COF materials but also provide a new fabrication strategy towards energy harvesting.

Graphical Abstract