Proton transport is essential and critical in a biological system and electrochemical devices. In particular, the fundamental understanding of proton conduction mechanism in conducting medium is important to design the efficient proton conductor. The overwhelming majority of proton conducting medium is water (H₂O) which was intensively investigated because water can form the efficient hydrogen bonding networks by symmetric two proton donor and two acceptor sites resulting in degenerated proton conduction system (H₃O⁺+H₂O ⇔ H₂O+H₃O⁺). In this point of view, we believe that ammonia (NH₃) can be a next promising conducting medium due to its similar molecular system to water. Specifically, it shows a small molecular size (2.60 Å), three proton donor sites/ one acceptor site, and degenerated proton conduction system (NH₄⁺+NH₃ ⇔ NH₃+NH₄⁺). Considering the fluid phase of NH₃, a confined environment should be required to achieve NH₃ proton conductor. The porous crystalline metal-organic frameworks (MOFs), tunable solid, are emerging as a new class of solid electrolyte because of a considerable porosity and versatile sorptivity. In particular, the pore of MOFs is a suitable platform to confine the guest molecules. In addition, a simultaneous proton donation from framework to NH₃ can induce the conjugated acid-base system in the pores.

Here, we show, for the first time, proton conductivity through the simultaneously confined NH₃ in MOFs by NH₃ adsorption. We choose highly stable Al-based MOFs consisting of one-dimensional channel and MO₄(OH)₂ secondary building units (SBUs) interconnected by dicarboxylate groups. Fuethermore, we can tune the pore environment by using the different fuctionla groups of ligand. We found cooperative ammonia adsorption with simultaneous ammonium formation and the highly enhanced proton conductivity as NH₃ pressure increases. Tthe structure analysis of MOFs incorporating NH₃ by Rietveld refinement and dynamic motion study of confined NH₃ by ²H solide-state NMR help to understand proton conduction mechanism. These results clearly support the Grotthuss mechanism not seen in bulk NH₃ system. We believe that this research may provide a design strategy for material using NH₃ as a conducting media as well as an energy carrier.