Macromolecular Polyethynylbenzonitrile Precursor-Based Porous Covalent Triazine Frameworks for Superior High-Rate High-Energy Supercapacitors.

Porous covalent triazine framework (CTF)-based carbon materials have gained increasing attention in energy-storage applications because of their tunable structure, high chemical stability, and rich heteroatom contents. However, CTFs have thus far been exclusively synthesized from small-molecular precursors and generally show unsatisfactory supercapacitive performance. We report herein the construction of a novel range of CTFs of significantly improved supercapacitive performance from polyethynylbenzonitrile (PEBN) as a unique macromolecular precursor for the first time by ionothermal synthesis. CTF-800 synthesized at the optimized condition (800 °C; ZnCl2/PEBN mass ratio of 3:1) shows a nanosheet-like morphology with a high yield (∼90%), high nitrogen content (>5.8%), high specific surface area (1954 m2 g-1), and optimized micropore to meso/macropore surface area ratio (42:58). As the electrode material for supercapacitor application, CTF-800 exhibits a high specific capacitance of 628 F g-1 at 0.5 A g-1, high-rate performance (71% of capacitance retention at 50 A g-1), and excellent cyclic stability (96% of capacitance retention over 20 000 cycles) in a three-electrode system with aqueous 1 M H2SO4 electrolyte. Symmetric supercapacitor devices have been further fabricated with CTF-800 in aqueous 1 M H2SO4, [EMIM][BF4], and LiPF6 electrolytes separately. The device with the aqueous electrolyte shows the highest capacitance of 448 F g-1 (at 0.5 A g-1) and a high energy density of 15.5 W h kg-1. The devices with [EMIM][BF4] and LiPF6 electrolytes exhibit exceptional energy densities of 70 and 78 W h kg-1, respectively, and retain energy densities of 41 and 45 W h kg-1, respectively, even at the high power density of 15 000 W kg-1, confirming their high-rate high-energy performance. Meanwhile, the device with [EMIM][BF4] electrolyte has also been demonstrated to operate well at various temperatures ranging from -20 to 60 °C with remarkable energy-storage performance.