High Enhancement in Proton Conductivity by Incorporating Sulfonic Acids into a Zirconium-Based Metal-Organic Framework via "Click" Reaction.

Taking a robust zirconium-based metal-organic framework, UiO-66, as a prototype, functional postmodification via the versatile Cu(I)-catalyzed azide-alkyne "click" reaction was carried out, and sulfonic acid groups were successfully grafted into its skeleton. Characterizations revealed that the MOF network was still well maintained after being treated by "clicked" modification. Investigations by electrochemical impedance spectroscopy measurements revealed that its proton conductivity increases exponentially up to 8.8 × 10-3 S cm-1 at 80 °C and 98% RH, while those of the UiO-66 and UiO-66-NH2 are only 6.3 × 10-6 and 3.5 × 10-6 S cm-1, respectively, at the same condition. Additionally, the continuous test shows it possesses long-life reusability. Such a remarkable enhancement on the proton conductivities and high performance in long-life reusability of the resultant MOF demonstrated that the "click" reaction is a facile reaction in postmodification of robust porous materials toward targeted applications, with which highly promising candidates of proton-conductive electrolytes for applying in proton-exchange-membrane (PEM) fuel cell can be achieved.