Heterogeneous Acid–Base Nanochannels in Covalent Organic Framework Membrane for Efficient Proton Conduction

Heterostructures with an ingenious integration of dual-material advantages have demonstrated extraordinary mass transport behaviors in energy conversion and separation applications. Here, a heterogeneous nanochannel (TpEB@TpPa-2SO3H) was constructed by alternately assembling acidic and alkaline covalent organic framework (COF) nanosheets containing different proton carriers (sulfonic acid or quaternary ammonium), denoted as TpPa-2SO3H and TpEB nanosheets, respectively. The resulting nanochannel membrane displays a significantly enhanced proton conductivity of 157.6 mS cm–1 at 85 °C and 100% RH, as compared to homogeneous TpPa-2SO3H (127.3 mS cm–1) and TpEB (0.27 mS cm–1) membranes. Theoretical calculations and experimental results demonstrate that the enhanced proton conductivity is attributed to optimized hydrogen-bonding networks and markedly reduced proton dissociation energy facilitated by acid–base pairs. Furthermore, the robust electrostatic interaction between the acidic nanosheet and alkaline nanosheet enables excellent water stability and structure stability of the TpEB@TpPa-2SO3H membrane. Notably, we find that this controlled alternating assembly significantly enhances proton conductivity within 1–3 layers, while the improvement of conductivity becomes negligible when the number of assembled nanosheets reaches eight in a single stacking process. In addition, the TpEB@TpPa-2SO3H lamellar membrane delivers an excellent hydrogen fuel cell performance, where peak power density and current density are up to 343 mW cm–2 and 1356 mA cm–2 at 60 °C and 100% RH, respectively. This work should provide a valuable insight for developing high-performance proton exchange membranes.