Covalent-Organic Frameworks (COFs) as Proton Conductors

Proton conductivity is the paramount property of proton-conducting materials that are playing significant roles in diverse electrochemical devices with applications in proton exchange membranes (PEMs) for fuel cells (PEMFCs). Considering the scarcity of fossil fuels, the development of clean and green renewable energy resources is in-demand across the globe. Toward this direction, the development of solid-state proton conductors is of significant interest. The higher structural tunability, lower density, good crystallinity, accessible well-defined pores, excellent thermal and chemical stability of covalent-organic frameworks (COFs) make them versatile platforms as proton conductors both under hydrous and anhydrous conditions. Taking advantage of such superior properties, the reports on proton-conducting COFs have been increasing swiftly since 2014, which demands a summarization and comprehensive discussion for "at a glance" visualization and further development. In this review, the COFs are showcased as a newer class of solid-state proton-conducting material. A comprehensive discussion is presented by organizing the strategies taken to develop the proton-conducting COFs. Establishment of structure-function relationships and the implementation of COFs as proton conductors are discussed as well. Moreover, challenges and future prospects are presented elaborately and are critically analyzed.