Monomer-Integrated Self-Supporting Covalent Organic Framework Nanosheets Membrane with Commendable Proton Conductivity and Enhanced Stability

Covalent organic framework (COF) materials are expected to be good candidates for proton exchange membranes (PEMs) due to their abundant, designable, and ordered one-dimensional pores as well as good stability. In this work, disulfonic acid COF nanosheets TpBd-2SO3HBd were synthesized through interfacial polymerization using 1,3,5-triformylphloroglucinol (Tp) and 4,4′-diaminodiphenyl-3,3′-disulfonic acid (Bd-(SO3H)2) as reactants. Biphenylamine (Bd) was incorporated as a co-monomer to modulate the interlayer interactions between the nanosheets, resulting in the development of a self-supporting TpBd-2SO3HBd proton exchange membrane with superiorly comprehensive performances. The incorporation of Bd led to improvement of the crystallinity of TpBd-2SO3HBd nanosheets. Moreover, the reduction of the surface charge of the nanosheets, the weakening of interlayer electrostatic repulsion, and the enhancement of interlayer ordered stacking promoted the construction of intramembrane proton transfer channels with a substantial increase in the proton conductivity reaching 276.8 mS/cm (80 °C, 100% RH). Meanwhile, the self-supporting TpBd-2SO3HBd membranes exhibited excellent cycling stability, water stability, and chemical stability.