ACS applied materials & interfaces | 2019
Macromolecular Polyethynylbenzonitrile Precursor Based Porous Covalent Triazine Frameworks for Superior High-Rate High-Energy Supercapacitors.
Abstract
Porous covalent triazine framework (CTF) based carbon materials gain increasing attention in energy storage applications because of their tuneable 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 \uf0b0C; ZnCl2/PEBN mass ratio of 3:1) shows a nanosheet-like morphology with high yield (~90%), high nitrogen content (>5.8%), high specific surface area (1,954 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), 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, respectively. 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 oC with remarkable energy storage performance.