In field of electrochemistry, there has been a growing interest in the potential applications of proton-conducting metal-organic frameworks (MOFs). Therefore, how to design and synthesize MOFs with high proton conductivity is considered crucial. In this study, two examples of nitro-containing Cd-based MOFs, MOF-1 {[Cd3(TIPE)1.5(NO3)5Cl(H2O)2] ⋅ 17H2O}n and MOF-2 {[Cd(TIPE)0.5(nip)] ⋅ 10H2O}n (TIPE=1,1,2,2-tetrakis(4-(1H-imidazole-1-yl)phenyl)ethene, H2nip=5-Nitroisophthalic Acid), had been successfully designed and synthesized, and their proton-conducting properties were thoroughly investigated. Notably, both materials displayed peak proton conductivity at 98 % RH and 90 °C, exhibiting values of 9.13×10-3 and 3.00×10-3 S cm-1 for MOF-1 and MOF-2, respectively. The plausible proton conduction pathways and mechanisms were elucidated through structural analyses, water vapor adsorption studies, and the determination of activation energy (Ea) values. It was found that the difference in proton conductivity between MOF-1 and MOF-2 was mainly associated with the different water absorption rates of the samples. The uniqueness of this study was that for the first time conducted an in-depth study of the role of nitrate in proton conduction, providing new ideas for designing materials with excellent proton conductivity.
Keywords: Nitro groups; Proton conductivity; Synthesis and structure.
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