3D Covalent Organic Framework Membrane with Interactive Ion Nanochannels for Hydroxide Conduction

Abstract

Crystalline porous materials, known for their ordered structures, hold promise for efficient hydroxide conductivity in alkaline fuel cells with limited ionic densities. However, the rigid cross-linking of porous materials precludes their processing into membranes, while composite membranes diminish materials’ conductivity advantage due to the interrupted phases. Here, we report a self-standing three-dimensional covalent organic framework (3D COF) membrane with efficient OH-transport through its interconnected 3D ionic nanochannels. The large-area, homogeneously connected COF membrane, with an 8 cm diameter and 20 μm thickness, was prepared using an interface polymerization strategy assisted by sacrificial templates of a polyacrylonitrile membrane. At the microscopic level, the introduction of imidazolium salt-building units resulted in a noninterpenetrated structure of 3D COF, creating a 3D interactive continuous hydrophilic channel for OH^–-conduction. The 3D COF membrane demonstrated high conductivity (169 mS/cm at 80 °C, 100% humidity) and achieved a peak power density of 160 mW/cm² in H₂/O₂ single-cell tests. This COF interface polymerization strategy brings new possibilities to address the challenges of porous material membrane formation and is expected to advance their practical applications in the field of ion transport.