Enhancing Proton Conductivity of a 3D Metal–Organic Framework by Attaching Guest NH₃ Molecules

Abstract

By reaction of a newly designed organic ligand, [3-(naphthalene-1-carbonyl)-thioureido] acetic acid (CHC(O)NHC(S)NHCHCOOH; HL), with Cu(OAc), a metal-organic framework [(CuCuL)·3HO] (1) containing unique mixed-valence [CuCuL] subunits has been successfully synthesized and structurally characterized. MOF 1 displays a three-dimensional open framework bearing one-dimensional channels. Consequently, a new derivative MOF [CuCuL] -NH (2) is procured upon exposure of 1 to NH vapors from 28 wt % aqueous NH solution, which bears 2 NH and 4 HO molecules in accordance with the elemental and thermal analyses. Both 1 and 2 exhibit relatively high water stability, whose proton conduction properties under water vapor have been researched. Notably, 2 shows an ultrahigh proton conductivity of 1.13 × 10 S cm, which is 2 orders of magnitude larger than that of MOF 1 (4.90 × 10 S cm) under 100 °C and 98% RH. On the basis of the structural data, E values, HO and ammonia vapor absorptions, and PXRD measurements, the proton transfer mechanisms were suggested. This is an efficient and convenient way to obtain suitable and highly proton-conducting materials by attaching NH molecules.

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.…”

Metal–Organic Frameworks and Other Crystalline Materials for Ultrahigh Superprotonic Conductivities of 10−2 S cm−1 or Higher

“…In a different approach that attached the NH 3 molecules onto the framework, Li and co‐workers showed an improvement of proton conductivity by alternating the composition of the ambient gases (NH 3 and water vapor) . The proton conduction value reached 1.13×10 −2 S cm −1 with the influence of ammonia molecules instead of water, with which the proton conduction value was 4.90×10 −4 S cm −1 under 100 °C and 98 % RH conditions.…”

Enhancement of Aqua‐Ammonia Vapor on Proton Conduction for Two Water‐Tolerant Complicated Copper Cluster Compounds

“…It should be pointed out that we recently found that the structure of the 3D MOF [(Cu I 4 Cu II 4 (NCT) 4 )⋅3H 2 O] n (H 3 NCT=[3‐(naphthalene‐1‐carbonyl)‐thioureido] acetic acid) transformed after 2.5 hours of exposure to concentrated NH 3 ⋅H 2 O vapor (14.8 M). In contrast, the two complexes 1 and 2 prepared here maintained their structural stability under low concentration of NH 3 ⋅H 2 O vapor (0.005‐2.0 M).…”

“…Nevertheless, the related investigation on acyl thiourea carboxylate‐based complexes is relatively limited. Solely our laboratory lately reported the proton conductive properties of an acyl thiourea carboxylate‐based MOF [Cu I 4 Cu II 4 (NCTA) 4 ]⋅3H 2 O} n (H 3 NCTA=[3‐(naphthalene‐1‐carbonyl)‐thioureido] acetic acid) and its NH 3 ‐derivative [Cu I 4 Cu II 4 (NCTA) 4 ] n ‐NH 3 . We found that the NH 3 ‐derivative has a high proton conductivity of 1.13 × 10 −2 S cm −1 at 98% RH and 100 °C, which is much larger than that of [Cu I 4 Cu II 4 (NCTA) 4 ]⋅3H 2 O} n .…”