Weakly Humidity-Dependent Proton-Conducting COF Membranes.

Area of Science:

• Materials Science
• Electrochemistry
• Chemical Engineering

Background:

• Proton exchange membranes (PEMs) are crucial for fuel cells but perform poorly under low humidity.
• Covalent organic frameworks (COFs) offer potential for improved PEMs due to their tunable structures.
• Fabricating defect-free COF membranes is challenging due to material processability issues.

Purpose of the Study:

• To develop a novel method for synthesizing intrinsic proton-conducting COF (IPC-COF) nanosheets.
• To create robust and processable IPC-COF membranes for fuel cell applications.
• To evaluate the performance of these membranes under varying humidity conditions.

Main Methods:

• A bottom-up synthesis approach using diffusion and solvent co-mediated modulation in aqueous solutions.
• Controlled nucleation and in-plane growth of IPC-COF nanosheets (NUS-9).
• Facile fabrication of IPC-COF membranes from synthesized nanosheets.

Main Results:

• IPC-COF membranes exhibit crystalline, rigid ion nanochannels.
• Conductivity is weakly dependent on humidity (30-98% RH), remaining high.
• Membranes show 1-2 orders of magnitude higher conductivity than benchmark PEMs.
• Achieved prominent fuel cell performance (0.93 W cm⁻² at 35% RH and 80 °C).

Conclusions:

• The developed method enables the synthesis of defect-free IPC-COF nanosheets and membranes.
• IPC-COF membranes demonstrate superior water retention and Grotthuss mechanism-dominated proton conduction.
• These membranes offer a promising solution for efficient fuel cell operation under diverse humidity levels.