Increased proton conductivity of metal–organic framework micro-film prepared by a facile salt-free approach

An effective, mild, salt-free and in situ substrate growth approach to MOFs was developed using copper foil. Such a simple approach afforded a microfilm with proton-conducting properties under stable conditions. Copper was employed not only to allow for large arrays of MOFs, but also to allow the root of crystals to attach close enough to form a dense film. The thickness of the films was in the order of microns. The proton conductivity was increased from ∼10−6 (disk-shaped pellet of powder) to as high as ∼10−4 S cm−1 (microfilm). The σ value of the microfilm is 6.9 × 10−4 S cm−1 after being kept under 98% relative humidity (RH) for 3 days at room temperature which is one order of magnitude higher than previously reported data for HKUST-1 related materials.