Enhancing proton conductivity of a highly water stable 3D Sr(II) metal-organic framework by exposure to aqua-ammonia vapor

The proton conductivity of a 3D Sr(II) MOF, [Sr (mu(2)-H2PhIDC)(2)(H2O)(4)]center dot 2H(2)O (1) (H3PhIDC - 2-phenyl-4,5-imidazole dicarboxylic acid) is investigated under water and aqua-ammonia vapors, respectively. The experimental results reveal that the proton conductivity of 1 under aqua-ammonia vapor is 4.76 x 10(-2) S cm(-1), and approximately four orders of magnitude greater than that (1.91 x 10(-6) S cm(-1)) under water vapor at 98% RH and 90 degrees C. Based on the activation energy calculations, water and NH3 vapor absorptions and PXRD determinations, its proton-conduction mechanism is discussed. The time dependent measurements for 1 under water and aqua-ammonia vapors illustrate its ability to retain conductivity up to 20 h. This is an effective approach to improve proton conductivity of MOFs by changing the vapor environment. (C) 2018 Elsevier B.V. All rights reserved.