A water-stable metal-organic framework with highly acidic pores for proton-conducting applications.

Metal-organic framework (MOF) materials are a nontraditional route to ion conductors, but their crystallinity can give insight into molecular-level transport mechanisms. However, some MOFs can be structurally compromised in humid environments. A new 3D metal-organic framework, PCMOF-5, is reported which conducts protons above 10(-3) S/cm at 60 °C and 98% relative humidity. The MOF contains free phosphonic acid groups, shows high humidity stability, and resists swelling in the presence of hydration. Channels filled with crystallographically located water and acidic groups are also observed.