Guanidinium Cationic Covalent Organic Framework Nanosheet-Based Composite Anion Exchange Membranes with Enhanced Hydroxide Conductivity

Anion exchange membranes (AEMs) as the core component of anion exchange membrane fuel cells (AEMFCs) are responsible for hydroxide (OH–) transport and preventing fuel crossover. However, traditional polymer matrix AEMs typically suffer from low conductivity and poor stability, which has constrained the development of AEMFCs. Here, we report a series of composite AEMs by incorporating guanidinium cationic covalent organic frameworks (TpTGCl) into N,N,N’,N’-tetramethyl-1,4-phenylenediamine (TMPD)-cross-linked imidazolium-functionalized poly(ether ether ketone) (qPEEK) via the solution casting method. The positive charge repulsion induces the self-exfoliation of TpTGCl to achieve covalent organic framework nanosheets (CONs), whose favorable dispersion enables a maximum doping content of 15 wt %. The high density of guanidinium cation groups in TpTGCl contributed to an ideal ion exchange capacity (IEC) of 2.92 mmol/g for composite AEMs. Moreover, the continuous cation domain and the additional one-dimensional (1D) nanochannels within TpTGCl enabled rapid transport of OH–, resulting in a remarkable OH– conductivity of 101.04 mS/cm (80 °C, 100% RH) for the qPEEK/TpTGCl-10 composite membrane. Meanwhile, the composite AEMs also exhibited enhanced mechanical strength (112.18 MPa), dimensional stability (SR< 18%, 30 °C), and alkaline stability (83.16% OH– conductivity retention).