A CNT electrode with the CNT side down was placed at one edge of the MOF@CNT film so that it is electrically in contact with the MOF@CNT film, as well as it sticks out of the edge of the cover slip. The MOF@CNT film was soaked with an imidazolium ionic liquid (OMIM-Cl, EMIM-Cl, or OMIM-Br). A PTFE membrane was placed onto it as a separator, and soaked with the ionic liquid. Another CNT electrode with the CNT side up was placed at one edge of the membrane so that it sticks out of the coverslip. The CNT film on the membrane was placed on top with the CNT side down so that it is electrically in contact with the CNT electrode. Another microscope coverslip was placed on top. The top and bottom coverslips were pressed to each other by binder clips.