Efficient Proton Conduction through [N···X···N]+ Halogen Bond Coordination in Halogen-Bonded Organic Frameworks

Abstract

Advancing anhydrous proton-conducting materials is essential for the fabrication of high-temperature (>373 K) polymer electrolyte membrane fuel cells (HT-PEMFCs) and remains a significant challenge. Herein, halogen-bonded organic frameworks linked by [N···I··N]⁺ interactions are reported as outstanding high-temperature conductive materials. By incorporating carbazole groups into the monomers, two highly crystalline halogen-bonded organic frameworks (XOF-CSP/CTP) are constructed. These XOFs exhibit a high intrinsic conductivity (σ = 1.22 × 10⁻³ S cm⁻¹) under high-temperature anhydrous conditions. Doping the XOFs with H₃PO₄ allows the nitrogen sites and I⁺ sites on the pore walls to stabilize and tightly confine the H₃PO₄ network within the porous framework through hydrogen bonding, thereby enhancing proton conductivity under anhydrous conditions (σ = 1.02 × 10⁻² S cm⁻¹). Temperature-dependent curves and theoretical calculations indicate that proton transport is governed by a low-energy barrier hopping mechanism. These materials exhibit excellent stability and maintain high proton conductivity across a broad temperature range. This work provides a new platform for designing anhydrous proton-conducting materials with significant potential as high-temperature proton exchange membranes.