(263g) Fabrication of ZSM-5 Zeolite Nanosheet Tiled Membranes on Macroporous Polymer Substrates As Ion Separators for Redox Flow Batteries

The defect-free membranes of zeolites with 10-membered ring or 8-membered ring pore openings are theoretically capable of conducting proton with perfect metal ion rejection by the ion-sieving effects. In the recent years, membranes of MFI-type zeolites (10-membered ring) and T-type zeolites (8-membered ring) have been demonstrated with high proton/metal-ion selectivity and good ion conductivities to perform well as ion separators in all-vanadium and iron-chromium redox flow batteries (RFBs). However, the conventional polycrystalline zeolite membranes are difficult for practical applications because of the loss of proton/metal-ion selectivity through the non-selective intercrystalline spaces, large resistance to proton diffusion in the subnanometer channels over large lengths of thick and randomly ordered zeolite layers, needs of heavy and costly rigid supports for the fragile polycrystalline thin membranes, and the poor manufacturability and quality control of the membranes by the hydrothermal crystallization techniques. Here we report our recent work on the fabrication of ZSM-5 zeolite nanosheet tiled membranes on practically meaningful porous polymer substrates, characterizations of the membrane performance in proton-selective ion conductions, and evaluation of the membranes as ion separators in RFB operations. This research is focused on developing new methods for zeolite nanosheet synthesis to avoid the difficulty in preparing dispersible pre-activated nanosheets and formation of ultrathin multilayered nanosheet membranes to simultaneously achieve high proton selectivity and conductivity. The membranes are tested as ion separators for vanadium RFB operations.