Effective Approach to Promoting the Proton Conductivity of Metal–Organic Frameworks by Exposure to Aqua–Ammonia Vapor

We explored the proton conductivities of two 3D Co II metal–organic frameworks (MOFs), {[Co 3 ( m -ClPhIDC) 2 (H 2 O) 6 ]·2H 2 O} n [ 1; m -ClPhH 3 IDC = 2-( m -chlorophenyl)imidazole-4,5-dicarboxylic acid] and {[Co 3 ( p -ClPhHIDC) 3 (H 2 O) 3 ]·6H 2 O} n ( 2; p -ClPhH 3 IDC = 2-( p -chlorophenyl)imidazole-4,5-dicarboxylic acid), under water and aqua–ammonia vapors, respectively. The experimental results revealed that the proton conductivities of 1 and 2 at aqua–ammonia vapor were 2.89 × 10 –2 and 4.25 × 10 –2 S/cm, respectively, and approximately 2 orders of magnitude greater than those at water vapor. On the basis of the activation energy, water and ammonia vapor absorption, and powder X-ray diffraction patterns, their proton-conduction mechanisms have been discussed. We believe that this is a novel approach to drastically improving the proton conductivity of MOFs.