Alkali-Durable Covalent Organic Frameworks Carrying <i>In Situ</i> Ammonium as an Ionic Conductor toward Hydroxide Transport
Bowen Yang, Cunman Zhang
Abstract
Durable transport of hydroxide ions is currently required to develop alkaline electrolyzers for efficient and clean hydrogen production. In the present work, a self-standing TAPA-TFP covalent organic framework (COF) membrane is obtained by oil–water interface polymerization. It is subsequently ionized through in situ ammonium groups via Menshutkin reactions to prepare a N+-COF ionic conductor. Based on the strategy of charge delocalization, the symmetric benzene around the in situ ammonium in the N+-COF ionic conductor could protect the cations from alkali degradation. Meanwhile, the micro-ordered alignment of cationic clusters endows the N+-COF ionic conductor with desirable hydroxide ion conductivities of up to 54 mS·cm–1 at 80 °C with an ion exchange capacity of 1.54 meq·g–1. Furthermore, when this N+-COF ionic conductor acts as a potential anion exchange membrane (AEM), it shows that water uptake and dimensional changes remain equalized between hydrophilicity and structural stability. It has been found that the N+-COF membrane has excellent alkaline stability through 1H nuclear magnetic resonance analysis, showing slight degradation of the cations after immersion in 1 M NaOH at 80 °C for 30 days. The alkaline stability and high conductivity of the N+-COF ionic conductor highlight its prospects as an AEM to be further applied in continuous water electrolysis, alkaline fuel cells, and hydrogen development.