Proton‐Conducting MOFs and HOFs: From Structural Design to Proton Exchange Membrane Applications

ABSTRACT

Crystalline porous materials, particularly metal‐organic frameworks (MOFs) and hydrogen‐bonded organic frameworks (HOFs), have attracted considerable interest as proton‐exchange membranes (PEMs) for fuel cells owing to their structural tunability and well‐defined proton transport pathways. Although the proton‐conducting properties of MOFs and HOFs have been widely investigated, their comparative roles in PEMs and the underlying design principles remain insufficiently clarified. This review provides a comparative analysis of design strategies in MOFs and HOFs, focusing on the roles of coordination bonding and hydrogen bonding in framework stability and proton transport. Recent advances in structural engineering are summarized, including intrinsic functionalization, charge‐assisted hydrogen‐bond networks, and strategies based on hydrophilicity control, guest interactions, and structural flexibility. Developments in MOF‐ and HOF‐based composite membranes and lamellar self‐standing membranes are also discussed. Key challenges regarding scalable fabrication, operating stability, mechanistic understanding, and economic feasibility are outlined to guide the rational design of crystalline proton‐conducting materials for energy applications.