High Proton Conductivity and Spectroscopic Investigations of Metal–Organic Framework Materials Impregnated by Strong Acids

Abstract

Strong toluenesulfonic and triflic acids were incorporated into a MIL-101 chromium(III) terephthalate coordination framework, producing hybrid proton-conducting solid electrolytes. These acid@MIL hybrid materials possess stable crystalline structures that do not deteriorate during multiple measurements or prolonged heating. Particularly, the triflic-containing compound demonstrates the highest 0.08 S cm(-1) proton conductivity at 15% relative humidity and a temperature of 60 °C, exceeding any of today's commercial materials for proton-exchange membranes. The structure of the proton-conducting media, as well as the long-range proton-transfer mechanics, was unveiled, in a certain respect, by Fourier transform infrared and (1)H NMR spectroscopy investigations. The acidic media presumably constitutes large separated droplets, coexisting in the MIL nanocages. One component of proton transfer appears to be related to the facile relay (Grotthuss) mechanism through extensive hydrogen-bonding interactions within such droplets. The second component occurs during continuous reorganization of the droplets, thus ensuring long-range proton transfer along the porous structure of the material.

Brønsted Acidity in Metal–Organic Frameworks

“…213 Unlike in the previous case of MOF-74(Ni), the existence of both acids together with water molecules was unequivocally confirmed by elemental analyses (TsOH@MIL-101, MIL-101·1.1TsOH·2H 2 O; TfOH@MIL-101, MIL-101·6.7TsOH·15H 2 O). TsOH@MIL-101 only exhibited moderate proton conducting ability (8.0 × 10 −6 S cm −1 at 66°C and 100% RH), probably due to their weaker acidity, larger non-hydrogen-bonded phenyl groups, and small loading of both acid and water molecules.…”

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

“…[13] Interestingly, both water-mediated (s = 4.2 10 À2 S cm À1 at 98 % RH) and anhydrous proton conductivities (s = 1 10 À4 S cm À1 at 150 8C) were established in a single framework, that is, {[(Me 2 NH 2 ) 3 (SO 4 )] 2 [Zn 2 -(oxalate) 3 ]} n . [13] Interestingly, both water-mediated (s = 4.2 10 À2 S cm À1 at 98 % RH) and anhydrous proton conductivities (s = 1 10 À4 S cm À1 at 150 8C) were established in a single framework, that is, {[(Me 2 NH 2 ) 3 (SO 4 )] 2 [Zn 2 -(oxalate) 3 ]} n .…”

“…The conductivity of a material is predominantly determined by the proton mobility and concentration. [13] Considering the high performance of Nafion with its terminal sulfonic acid groups, it is desirable to include pendent sulfonic acid groups in the framework for high conductivity. The first approach involves the encapsulation of guest molecules (e.g., triazole, [7] imidazole, [8] histamine, [9] ammonium cations, [10] or hydronium ions [11] ) in the structures.…”

Proton‐Conductive 3D LnIII Metal–Organic Frameworks for Formic Acid Impedance Sensing

“…[15][16][17][18][19][20][21][22][23][24] Unlike semicrystalline or amorphousp olymers, the high crystallinity of MOFs is very suitable for studying protont ransport pathway and the conductionm echanism, demonstrating that protonc an transit through modified groups on the surfaceo ft he cavity (e.g., H 2 O, -SO 3 Ha nd -PO 3 H 2 )a nd guests in the cavity (e.g.,i midazole, histamine and ionic liquids). [5,16,[25][26][27][28] On the other hand, based on the outstanding advantagesofMOFs, the exploration of the practical application of electrically conductive MOFs has received extensive attention, especially in the field of chemoresistive sensors. [29][30][31][32][33][34] Representatively,D incǎ et al demonstrated an array of cross-reactive sensor for the identification of different typeso fv olatile organic compounds (VOCs).…”