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

Abstract

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.

Funding

Science and Technology Commission of Shanghai Municipality(20JC1414900)

National Natural Science Foundation of China(22271188)

China Postdoctoral Science Foundation(2020M681277)

Natural Science Foundation of Shanghai(23ZR1481100)

Shuguang Program of Shanghai Education Development Foundation and Shanghai Municipal Education Commission(22SG54)