Solid-State Proton Conduction Driven by Coordinated Water Molecules in Metal–Organic Frameworks and Coordination Polymers

As efficient alternative renewable energy resources, proton-exchange membrane fuel cells (PEMFCs) have received immense attention where proton-conducting materials act as PEMs for efficient proton migration. The recent past has witnessed considerable progress in the use of metal–organic frameworks (MOFs) and coordination polymers (CPs) as solid-state proton conductors (SSPCs) due to their structural superiority and architectural diversity. In order to impart proton conductivity, a variety of intrinsic and extrinsic proton sources have been installed onto these frameworks; however, reports on proton conduction where metal-coordinated water molecules act as solely intrinsic proton sources by virtue of their enhanced acidity are largely unexplored. The key examples of proton conduction driven by coordinated water molecules discussed in this Perspective present some unique features of MOFs and CPs as SSPCs, displaying a wide range of proton conductivity. The scope of works with plausible design principles that are urgently required to be investigated is also highlighted.