Defect Engineering in a Metal–Organic Framework System to Achieve Super-Protonic Conductivity

Controlled incorporation of missing-linker defect sites could be achieved in four sister metal–organic frameworks (MOFs) of MOF-808, namely, MOF-808 A–D via modulated synthesis. An impressive enhancement in proton conductivity is observed in these sister MOFs (increase from 10–3 to 10–1 S cm–1) as compared to a highly crystalline, low-in-defect variant of MOF-808. MOF-808 C, having optimized defect density, shows a proton conductivity of 2.6 × 10–1 S cm–1 at 80 °C and 98% relative humidity–the highest value reported to date for pure MOF-based proton conductors without extensive structural modifications. The introduction of defects induces super-protonic conductivity by modifying different properties, like porosity, water sorptivity, and acidity. Furthermore, an assembly of this super proton-conducting MOF with Pt─a versatile hydrogen evolution reaction (HER) catalyst, has been studied with the objective to influence the catalytic activity. This MOF-catalyst assembly was found to have lower overpotential requirements, owing to an increase in local acidity and efficient proton management around the catalyst.