Pore Geometry and Surface Engineering of Covalent Organic Frameworks for Anhydrous Proton Conduction

Abstract

Developing new materials for anhydrous proton conduction under high-temperature conditions is significant and challenging. Herein, we create a series of highly crystalline covalent organic frameworks (COFs) via a pore engineering approach. We simultaneously engineer the pore geometry (generating concave dodecagonal nanopores) and pore surface (installing multiple functional groups such as À C=NÀ , À OH, À N=NÀ and À CF 3 ) to improve the utilization efficiency and hostguest interaction of proton carriers, hence benefiting the enhancement of anhydrous proton conduction. Upon loading with H 3 PO 4 , COFs can realize a proton conductivity of 2.33 × 10 À 2 S cm À 1 under anhydrous conditions, among the highest values of all COF materials. These materials demonstrate good stability and maintain high proton conductivity over a wide temperature range (80-160 °C). This work paves a new way for designing COFs for anhydrous proton conduction applications, which shows great potential as high-temperature proton exchange membranes.

Recent Progress of Crystalline Porous Frameworks for Intermediate-Temperature Proton Conduction

“…Azo groups (N = N) were introduced into COF to narrow the pore size and lock H 3 PO 4 with hydrogen bonds (Figure 13). 108 −CF 3 groups were decorated onto the COF skeleton to tune the pore hydrophobicity. Trifluoromethyl groups have totally changed the chemical environment of channels of the COF.…”

“…Illustration of the pore engineering approach to construct COFs for anhydrous proton conduction. Reproduced or adapted with permission from ref . Copyright 2023 Wiley-VCH.…”

Enhanced stability and ultrahigh proton conductivity of hydrogen-bonded organic frameworks

“…In the past two decades, researchers have conducted a large number of studies on the proton conductivity of crystalline materials such as inorganic solid acids, polyoxometalates (POMs), organic crystals, metal-organic frameworks (MOFs)/ porous coordination polymers (PCPs) and covalent organic frameworks (COFs). [4][5][6][7][8][9][10][11][12][13] The results show that they have great application potential as PEM materials because their clear structures enable people to understand their proton conduction mechanism and further improve their proton conduction performance. Among them, MOFs and COFs have become a research hotspot in the field of proton conduction due to their advantages of diverse structures, designable synthesis, high porosity, large specific surface area, regular channels, adjustable pore size and easy post-modification.…”

Design, Preparation, and High Intrinsic Proton Conductivity of Two Highly Stable Hydrazone-Linked Covalent Organic Frameworks

“…Du et al 37 designed and synthesized one COF with hierarchical pores (PIL0.5@ mTpPa-SO 3 H) with σ up to 0.102 S•cm −1 (90 °C, 100% RH). Zhang's group 38 designed several novel COFs by pore engineering and discovered that H 3 PO 4 @NKCOFs exhibited high anhydrous σ of 2.33 × 10 −2 S•cm −1 at 170 °C after loading with phosphoric acid. These examples demonstrate the potential, albeit challenging, of preparing COFs with high proton conductivity.…”