Effective Approach to Promoting the Proton Conductivity of Metal–Organic Frameworks by Exposure to Aqua–Ammonia Vapor

Abstract

We explored the proton conductivities of two 3D Co metal-organic frameworks (MOFs), {[Co(m-ClPhIDC)(HO)]·2HO} [1; m-ClPhHIDC = 2-(m-chlorophenyl)imidazole-4,5-dicarboxylic acid] and {[Co(p-ClPhHIDC)(HO)]·6HO} (2; p-ClPhHIDC = 2-(p-chlorophenyl)imidazole-4,5-dicarboxylic acid), under water and aqua-ammonia vapors, respectively. The experimental results revealed that the proton conductivities of 1 and 2 at aqua-ammonia vapor were 2.89 × 10 and 4.25 × 10 S/cm, respectively, and approximately 2 orders of magnitude greater than those at water vapor. On the basis of the activation energy, water and ammonia vapor absorption, and powder X-ray diffraction patterns, their proton-conduction mechanisms have been discussed. We believe that this is a novel approach to drastically improving the proton conductivity of MOFs.

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

“…At 68 %R Ha nd 25-100 8C, the conductivities are 2.77 10 À8 ,6 .44 10 À7 and 1.50 10 À5 Scm -1 under 25, 70 and 100 8C, respectively (Figure S7). The optimum conductivity (8.95 10 À4 Scm -1 )o fZZU-1 is distinctly higher than that of conventional MOFs, [9,18,52] but slightly lower than that of other conductive materials. Ta ble S4 summarized some protonc onductivities under high humidityt est conditions.…”

“…[5,7,8] Metal-organic frameworks (MOFs) assembled from metals and organic ligands have shown promising application prospects in this field due to the special characteristicso fp orosity,o rderliness, modulars ynthesis route and robustness. [9][10][11][12][13] Kanda et al first reported ap rotonc onductive MOFs in 1979, [14] and since then, these materials have becomeanew field of research, making significant progress. [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).…”

A Highly Stable Two‐Dimensional Copper(II) Organic Framework for Proton Conduction and Ammonia Impedance Sensing

“…The data demonstrated that the activatione nergies at 68 and 98 %R Ha re 0.50 and 0.18 eV,r espectively (Figure 9). This means the observed proton conductivities follow the Vehicle mechanism at 68 %R H and Grotthus mechanism at 98 %R H. [36,37] The higher activation energy of 0.50 eV indicates that its proton conduction origi-nates from the movemento fe xotic water and ammonia molecules inside the layersa ccompanied by NH 4 + [27,28] the exotic water and ammonia molecules, and protonation of the media from the aqua-ammonia vapor exhibit as ynergistic effect on the proton conduction process. This can explain why relatively high RH is favorable for ammonia identification.…”

“…Thus, it leads to the optimized protonconductivity for 1 of 1.50 10 À3 Scm À1 .A sl isted in Ta ble 2, althought he optimized conductivity value is smaller than that of severalr ecent MOFs, [38][39][40][41] this value can be compared to that of some previousM OFs under similar tested conditions, [41][42][43][44][45][46] and is remarkably highert han that of four imidazole dicarboxylate-based Co II MOFs and other MOFs. [27,28,47] It is illustrated again that the structural advantage of MOF 1 is the a large amount of uncoordinated carboxylate units between the layers forprotontransfer.…”

“…Second, we were inspired by our recent findings about remarkably increasing the protonc onductivities of four Co II imidazole dicarboxylate-based MOFs with increasingc oncentrationso fa qua-ammonia vapor. [27,28] Importantly,t he increasing amplitude of proton conductivitiesi sp roportionalt ot he concentration of aqua-ammonia vapor.T his suggests that this kind of MOF can be used forthe electrochemical sensing of ammonia vapor.…”