Importantly, both reduced and oxidized states observed at negative and positive potentials, respectively, are sustained for longer than a day at room temperature (see Supplementary Information 2, Section S1), which represents the bistability of the system, a prerequisite for energy storage. MOF-CNT battery cell composed of a MOF@CNT film on a PTFE membrane, another PTFE membrane as the separator, and a CNT film prepared on a membrane as the counter electrode, all of which are soaked with a pure ionic liquid (e.g. OMIM-Cl) and sandwiched by two glass coverslips. For more detail, see the Methods section.