Design and Assembly of Conductive Covalent Organic Frameworks for Proton Exchange Membrane Application

To develop proton exchange membranes (PEMs) with robust structure stability and remarkable proton conductivity and explore their application in PEMs fuel cells have significant implications for realizing reduced carbon emission and environmental pollution. Covalent organic frameworks (COFs), as crystalline porous polymer material composed of organic monomers and connected by covalent bond, possess specific framework, inherent porosity, adjustable functional group and eminent thermal/chemical structure stability. Therefore, COFs display prominent superiorities in constructing rigid ordered proton transfer channels and improving fuel cell performance long-term durability. In this review, the proton conduction properties of extrinsic proton-conductive COFs (incorporating carriers into the pore), intrinsic proton-conductive COFs (introducing conductive groups on the backbone) and combined extrinsic/intrinsic proton-conductive COFs in the form of pressed pellets are discussed in detail. Meanwhile, proton-conductive COFs related PEMs, including COFs-related polymer-based composite membranes, COFs-based composite membranes and self-supporting COFs membranes are also systematically summarized. In addition, the existing challenges are analyzed and future outlooks are addressed.