Atomic engineering in covalent organic frameworks for high-performance proton conduction

Abstract

Proton exchange membrane fuel cells (PEMFCs) are promising for addressing energy and environmental challenges due to their efficiency and low emissions. The proton exchange membrane is critical for PEMFC performance, demanding high proton conductivity, stability, and durability. While Nafion is widely used, its limitations under high temperatures and low humidity have spurred research into alternative materials, such as covalent organic frameworks (COFs). COFs, with their tunable structures, high surface areas, and thermal stability, offer significant potential for proton conduction. In this study, we synthesized a series of pyrene-based 2D COFs with varying phenolic hydroxyl group contents, demonstrating their high crystallinity, porosity, and stability. Proton conduction tests were carried out on phosphoric acid-doped COFs, the results revealed that proton conductivity increased with a higher number of phenolic hydroxyl groups in the 1D channels of the COFs. Under optimized conditions, the highest proton conductivity reached 1.09 × 10⁻¹ S cm⁻¹ at 373 K and 98% relative humidity, which is among the highest values ever reported for proton-conducting COFs. This work highlights the role of hydroxyl groups in proton conduction and provides insights for designing advanced proton-conducting materials for fuel cell applications.