Remarkably enhancing proton conductivity by intrinsic surface sulfonation of a pyrazine-linked covalent organic framework

• Published in: Science China materials Vol. 67; no. 1; pp. 125 - 133
• Main Authors: Luan, Tian-Xiang, Wang, Qiurong, Zhang, Pengtu, Li, Wanchao, Kong, Shuo, Feng, Yijing, Yuan, Shiling, Li, Pei-Zhou
• Format: Journal Article
• Language: English
• Published: Beijing Science China Press 01.01.2024; Springer Nature B.V
• Subjects: Chemistry and Materials Science; Chemistry/Food Science; Contact angle; Density functional theory; Electrolytes; Materials Science; Nitrogen atoms; Porous materials; Protons; Pyrazines; Relative humidity; proton conduction; pyrazine linkage; surface modification; covalent organic framework; electrolyte
• ISSN: 2095-8226; 2199-4501
• DOI: 10.1007/s40843-023-2685-5

Enhancing the proton conductivity and long-life reusability of the electrolytes by surface modification is a feasible way to fabricate effective proton-conductive electrolytes for the practical application of proton exchange membrane. Herein, on account of its framework robustness and the proton-accepting nitrogen atoms uniformly located in its skeleton, a pyrazine-based covalent organic framework (COF) was selected as a masterplate, and its tert -butyl-absent COF structure, PyHATP-1, was constructed. Experimental results reveal that after its intrinsic pore surface is treated by post-sulfonation, the proton conductivity of the sulfonated sample, PyHATP-1-SO 3 H, exponentially increases to 1.3 × 10 −3 from 7.2 × 10 −6 S cm −1 of PyHATP-1 at 353 K and 98% relative humidity. Moreover, while loading H 3 PO 4 molecules into the skeletons, the sulfonated H 3 PO 4 @PyHATP-1-SO 3 H not only displays a remarkable increase in the proton conductivity (0.88 × 10 −1 S cm −1 ) compared with the unsulfonated H 3 PO 4 @PyHATP-1 (2.0 × 10 −3 S cm −1 ), but also exhibits a longer reusability. Contact angle tests and density functional theory calculations reveal that its remarkable enhancement in the proton conductivity and long-life reusability are attributed to the post-sulfonation of the pore surface, which significantly improves the affinity towards proton carriers (H 2 O and H 3 PO 4 molecules). This work demonstrates that by modifying the intrinsic surface of porous materials, effective proton-conductive electrolytes with high proton conductivity and long-life reusability can be achieved.