Intercrystalline defect healing in polycrystalline MOF membranes by pressurized counter-diffusion secondary growth

Abstract

The significance of membranes in the future of sustainable energy and emission reduction is universally recognized, as they play a crucial role in processes such as hydrogen production, decarbonization, and power generation. Molecular sieving polycrystalline MOF membranes hold considerable promise among various membrane materials due to their selective pore structures. However, the full potential of molecular sieving is compromised by the unavoidable defect formation during membrane synthesis, resulting in reduced membrane separation efficiency, stability, repeatability, and scalability. Here, we introduced a novel intercrystalline healing process utilizing pressurized counter-diffusion to address this long-lasting challenge of polycrystalline membranes and to achieve microstructure evolution and heal typical intercrystalline defects in MOF membranes. This method enables the controlled infiltration of precursors into defects for crystal growth, followed by sealing the unselective gaps through Ostwald ripening. Therefore, a compact and uniform MOF layer with significantly reduced intercrystalline defects can be formed. The final membrane demonstrates a 91 % reduction in total defect volume, while most remaining defects become isolated with less impact on the membrane selectivity. In the healed ZIF, the H₂/N₂ selectivity improved over 15-fold compared to the initial ZIF membrane, surpassing peers and achieving an optimal balance in the permeability-selectivity trade-off. Similar improvements were observed for other polycrystalline MOF membranes (e.g., CuBTC), highlighting the universality of addressing the common defect issue in various MOF and polycrystalline membranes.