Proton-Conducting Hydrogen-Bonded Organic Frameworks

Solid-state proton-conducting materials play essential roles in various electrochemical devices, including fuel cells as solid electrolytes. Recently, research on hydrogen-bonded organic frameworks (HOFs) has gained considerable momentum in diverse applications, as several of them show high stability with permanent microporosity. The inherent well-defined H-bonded networks in HOFs make them versatile platforms as solid-state proton conductors exhibiting conductivities as high as 10–1 S cm–1. In this Focus Review, we present the development of HOFs as proton conductors while briefing early reports on proton-conducting H-bonded organic systems. Reports on proton conductivity with other terminologies, such as supramolecular organic frameworks (SOFs), porous organic salts (POSs), or porous molecular crystals (PMCs), are also taken into consideration. All efforts have been made to organize and classify the proton-conducting HOFs with a deeper insight into the design principle and critical features in realizing such conduction properties. The advantages, potential challenges, and prospects of HOFs as proton conductors are discussed.