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

Abstract The proton conductivity of a 3D Sr(II) MOF, [Sr ( μ 2 -H 2 PhIDC) 2 (H 2 O) 4 ]·2H 2 O ( 1 ) (H 3 PhIDC = 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 × 10 −2  S cm −1 , and approximately four orders of magnitude greater than that (1.91 × 10 −6  S cm −1 ) under water vapor at 98% RH and 90 °C. Based on the activation energy calculations, water and NH 3 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.