title: Promotion of low-humidity proton conduction by controlling hydrophilicity in layered metal-organic frameworks.
abstract: We controlled the hydrophilicity of metal-organic frameworks (MOFs) to achieve high proton conductivity and high adsorption of water under low humidity conditions, by employing novel class of MOFs, {NR(3)(CH(2)COOH)}[MCr(ox)(3)]·nH(2)O (abbreviated as R-MCr, where R = Me (methyl), Et (ethyl), or Bu (n-butyl), and M = Mn or Fe): Me-FeCr, Et-MnCr, Bu-MnCr, and Bu-FeCr. The cationic components have a carboxyl group that functions as the proton carrier. The hydrophilicity of the cationic ions was tuned by the NR(3) residue to decrease with increasing bulkiness of the residue: {NMe(3)(CH(2)COOH)}(+) > {NEt(3)(CH(2)COOH)}(+) > {NBu(3)(CH(2)COOH)}(+). The proton conduction of the MOFs increased with increasing hydrophilicity of the cationic ions. The most hydrophilic sample, Me-FeCr, adsorbed a large number of water molecules and showed a high proton conductivity of ~10(-4) S cm(-1), even at a low humidity of 65% relative humidity (RH), at ambient temperature. Notably, this is the highest conductivity among the previously reported proton-conducting MOFs that operate under low RH conditions.
authors.affiliation: Division of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto, Japan.
authors.forename: Masaaki
authors.initials: M
authors.lastname: Sadakiyo
authors.forename: Hisashi
authors.initials: H
authors.lastname: Okawa
authors.forename: Akihito
authors.initials: A
authors.lastname: Shigematsu
authors.forename: Masaaki
authors.initials: M
authors.lastname: Ohba
authors.forename: Teppei
authors.initials: T
authors.lastname: Yamada
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kitagawa