Superprotonic Conductivity of a UiO‐66 Framework Functionalized with Sulfonic Acid Groups by Facile Postsynthetic Oxidation

Abstract

Facile postsynthetic oxidation of the thiol-laced UiO-66-type framework UiO-66(SH) 2 enabled the generation of UiO-66(SO 3 H) 2 with sulfonic acid groups covalently linked to the backbone of the system. The oxidized material exhibited a superprotonic conductivity of 8.4 10 À2 S cm À1 at 80 8C and 90 % relative humidity, and long-term stability of the conductivity was observed. This level of conductivity exceeds that of any proton-conducting MOF reported to date and is equivalent to the conductivity of the most effective known electrolyte, Nafion.

Designing UiO-66-Based Superprotonic Conductor with the Highest Metal–Organic Framework Based Proton Conductivity

“…Furthermore, it could also be confirmed from ICP-AES analysis that, only half of the '-NH 2 ' groups of UiO-66-NH 2 are modified in both cases (PSM 1 and PSM 2). These results also enlighten the fact of low Brønsted acid loading (almost one fourth) when compared with the similar system UiO-66(SO 3 ) 2 , reported by Phang et al 44 As the PSM is supposed to increase steric bulk inside the cavities of PSM 1 and PSM 2 from that of UiO-66-NH 2 parent MOF, large variation in the permanent porosity could be expected. N 2 gas sorption measurement at 77 K was used as the tool to determine permanent porosity of all the MOFs (Figure 4(a)).…”

“…61 Few years ago, Hong and coworkers showed UiO-66(SO 3 H) 2 to possess conductivity of 8.4×10 -2 Scm -1 . 44 High loading of pendant sulphonic acid groups played crucial role behind this observed proton conductivity. Li and coworkers developed another UiO-66 based proton conductor by its functionalization.…”

“…[30][31][32] In this scenario, metal organic frameworks (MOFs) stand as a connecting bridge between inorganic cluster containing compounds and organic polymers in terms of detailed structural information from crystal structure and efficiency of proton conduction. [37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53] These MOFs, being polymeric hybrid of organic linker molecule and metal ions, cultivate some of the useful properties of both. 3,6 They have high thermal stability, tunable dimensionality of channels, provision to modify the organic linkers to impart selective functionality, scope of loading charge carrier ion and also the provision to incorporate Brønsted acidity inside the MOF cavity.…”

High Electrical Conductivity in a 2D MOF with Intrinsic Superprotonic Conduction and Interfacial Pseudo-capacitance

“…23,24 Third, the introduction of functional groups to adjust the pore microenvironments of MOFs is another effective approach to improve their proton conductivity. 25 Several specific base/acid groups, including imidazole, 26,27 NH 3 , 28 sulfonic, 29,30 phosphonic, 31 and carboxylic groups, 32,33 have been incorporated into MOFs for enhanced proton conductivity, as they can tune the hydrophilicity of the pore surface, confer protons, and form hydrogen bonds as the proton migration pathway. 34 It is also worth noting that although three-dimensional (3D) protonconductive MOFs have been developed, 2D proton-conductive MOFs are rarely reported.…”

Robust Crystalline Hybrid Solid with Multiple Channels Showing High Anhydrous Proton Conductivity and a Wide Performance Temperature Range

“…Significant effort has been put into researching new nonvolatile and easy to manufacture solid electrolytes to make fuel cells with higher energy density and a longer cycling lifetime. To this end, organic polymers, inorganic materials, metal‐organic‐frameworks/porous coordination polymers (MOFs/PCPs) and covalent organic frameworks (COFs) have been developed, as well as porous solids doped by nonaqueous molecules such as the nonvolatile acids H 2 SO 4 and H 3 PO 4 and organic aryl molecules …”