Synthesis of a Nitrile- and Ether-Rich Covalent Organic Framework as a Filler and Its Application for Proton Exchange Membranes.

In the fabrication of proton exchange membranes (PEMs), incorporating nanomaterials into the polymer matrix is a promising strategy for enhancing membrane stability. However, this approach often results in a trade-off with proton conductivity. To address this limitation and develop efficient additives, we synthesized a novel covalent organic framework with a high density of ether and nitrile groups (COF-EN) via nucleophilic substitution as a nanofiller. This nanofiller was specifically designed to enhance both the proton conductivity and the stability of the membranes. The chemical structure of the synthesized COF-EN was confirmed through various analytical techniques, and it was subsequently integrated into a sulfonated poly(ether ether ketone) (SPEEK) matrix to fabricate advanced composite membranes. The resulting membranes demonstrated enhanced dimensional, thermal, and oxidative stability due to strong intermolecular interactions between the SPEEK chains and COF-EN. Additionally, the polar nitrile and ether groups in the COF-EN facilitated water absorption in the membranes, contributing to improved proton conductivity. As a result, SPEEK/COF-EN_3 exhibited a 2.3-fold increase in power density compared to the pristine SPEEK membrane, establishing COF-EN as an effective nanofiller for PEM fabrication.