High Proton Conductivity of a Bismuth Phosphonate Metal-Organic Framework with Unusual Topology

Despite the interest in proton exchange membrane (PEM)technologies(fuel cells and electrolyzers) for energy applications, the low stabilityof the electrolyte materials under working conditions (i.e., humidityand temperature) is one of their major limitations. Metal-organicframeworks (MOFs) have recently emerged as promising electrolytesdue to their higher stability compared with the currently appliedorganic polymers, proton conductivity, and outstanding porosity. Here,a novel robust Bi phosphonate MOF (branded as IEF-7) was successfullysynthesized and fully characterized, exhibiting an unusual topologydue to the irregular coordination geometry of the bismuth cations.Furthermore, IEF-7 exhibited potential porosity, very high chemicaland thermal stability, and free -PO3H groups involvedin its ultrahigh proton conductivity, reaching 1.39 x 10(-2) S cm(-1) at 90 degrees C and 90% relativehumidity for, at least, 3 cycles. In order to improve the consolidationand shaping of the powder for testing its ion conductivity properties,a highly MOF-loaded composite (90 wt %) was prepared by adding a protonconductive sulfonated polysulfone binder. The proton conductivityof the resulting composite was in the same order of magnitude as thecompacted MOF powder, making this polymeric composite electrolytevery promising for PEM technologies.

Automated summary

Despite the limitations of low stability in proton exchange membrane (PEM) technologies, metal-organic frameworks (MOFs) have emerged as promising electrolytes due to their higher stability, proton conductivity, and porosity. In this study, a novel bismuth phosphonate MOF (IEF-7) with unusual topology was successfully synthesized and characterized. IEF-7 exhibited high stability, potential porosity, and ultrahigh proton conductivity, making it a promising electrolyte for PEM technologies.