Fabrication of ZIF-7 Membranes by Electrochemical Deposition in Mixed Solvent for Efficient Helium Separation

Metal organic framework (MOF) membranes represent one of the most promising materials for helium (He) separation membranes. However, conventional fabrication methods using high-boiling-point solvents often generate defects during activation. This work employs a mixed-solvent-assisted electrodeposition method for ZIF-7 membranes wherein the DMF solvent lowers the ligand deprotonation energy barrier and the methanol solvent increases the solution supersaturation, synergistically enhancing the nucleation rate and nucleation density. Concurrently, the introduction of methanol leads to reduced precursor solubility, thereby reducing the ZIF-7 growth rate. Additionally, the use of methanol allows activation of the ZIF-7 via mild conditions, suppressing the formation of defects. As a result, ultrathin (160 nm) ZIF-7 membranes with low crystallinity and reduced intercrystalline defects are fabricated for the first time, achieving efficient He separation. The membrane on anodic aluminum oxide (AAO) demonstrates a He/N 2 selectivity of 261.2, which is nearly an order of magnitude higher than other reported He-selective MOF membranes. Continuous operation exceeding 144 h confirms exceptional stability. Successful fabrication on porous ceramic substrates with maintained separation performance underscores application potential of our strategy.