Proton conductivity studies on five isostructural MOFs with different acidity induced by metal cations

Abstract

Five isostructural metal-organic frameworks, [M1.5(L)(bpy)(DMF)]·H2O (M = Mn (1), Co(2), Ni(3), Zn(4), Cd(5); L = 3-(3,5-dicarboxylpheny)-5-(3-carboxylphenyl)-1H-1,2,4-triazole, bpy = 2,2’-bipyridine) have been synthesized and characterized. The same structure and similar proton...

Metal–Organic Frameworks for Ion Conduction

“…Functional groups with lower p K a exhibit higher proton conductivity than their analogs with higher p K a ; for example, the p K a values for −NH 2 , −H, −OH, and −COOH are 4.74, 4.19, 4.08, and 3.62, while, the corresponding proton conductivities of MOFs grafted with the above functional groups are 2.3×10 −9 , 2.3×10 −8 , 4.2×10 −7 , and 2.0×10 −6 S cm −1 , respectively, at 25 °C and 95 % RH [45] . For isostructural MOFs with different metal centers, [M 1.5 (L)(bpy)(DMF)]⋅H 2 O, [46] where L=3‐(3,5‐dicarboxylpheny)‐5‐(3‐carboxylphenyl)‐1 H ‐1,2,4‐triazole, bpy=2,2′‐bipyridine, and M=Mn, Co, Ni, Zn, or Cd, the conductivities decrease in the order of Mn−MOF>Zn−MOF>Cd−MOF>Co−MOF>Ni−MOF, in accordance with their acidities.…”

“…Functional groups with lower pK a exhibit higher proton conductivity than their analogs with higher pK a ; for example, the pK a values for À NH 2 , À H, À OH, and À COOH are 4.74, 4.19, 4.08, and 3.62, while, the corresponding proton conductivities of MOFs grafted with the above functional groups are 2.3 × 10 À 9 , 2.3 × 10 À 8 , 4.2 × 10 À 7 , and 2.0 × 10 À 6 S cm À 1 , respectively, at 25 °C and 95 % RH. [45] For isostructural MOFs with different metal centers, [M 1.5 (L)(bpy)(DMF)]•H 2 O, [46] where L = 3-( 3 type nets, originally studied for their magnetic properties, [47] were first introduced into solid-state proton conductors by Kitagawa et al [48] The oxalate ion (ox 2À ) directly interacts with homo-/ mixed-metal centers to build stable one-dimensional, [48] twodimensional, [36,37] and three-dimensional [49,50] frameworks with high proton conductivities ranging from 10 À 4 to 10 [36] (NH 4 ) 4 [MnCr 2 (ox) 6 ] 3 •4 H 2 O, [51] and {NH(prol) 3 }[M II Cr III (ox) 3 ]. [50] Unfortunately, the oxalic acids in these compounds are totally coordinated to metal ions, preventing the release of free protons as possible carriers; however, the rich O atoms facilitate hydrogen bonding.…”

High proton conductivity modulated by active protons in 1D ultra-stable metal–organic coordination polymers: a new insight into the coordination interaction/ability of metal ions

“…29 For metal ions, besides the ionic radius and the ionic potential, their coordination interaction/ability has a considerable impact on the physicochemical properties of MOCPs/MOFs in theory, with no exception for proton conduction, whereas too little attention has been paid to its influence in practice. 30 As a result, there remains a necessity to clarify the effect of the coordination interactions/abilities of metal ions on the proton conductivities of MOCPs/MOFs.…”

Enhancing Proton Conductivity of Nafion Membrane by Incorporating Porous Tb-Metal–Organic Framework Modified with Nitro Groups

“…With the development of economies and the continuous burning of fossil fuels, the increasingly serious global energy crisis forces people to develop clean renewable energy. , Proton exchange membrane fuel cells (PEMFCs) are considered promising energy candidates for a wide range of applications such as electric vehicles, portable electronics, and smart power grids − due to their high power density and environmental protection (only water is the combustion product). The proton exchange membrane (PEM), which can selectively allow protons generated from the cathodic reactions to transfer to the anode and maintain the continuity of the battery reaction, is one of the most important components of PEMFCs.…”