Sulfonated Sub-Nanochannels in a Robust MOF Membrane: Harvesting Salinity Gradient Power.

We developed a robust, crack-free ultrathin zeolite- imidazole framework (ZIF-8) membrane in-built with a sulfonate-ion-containing polymer (ZIFHep) via a vapor-assisted in situ conversion process. The sulfonated sub-nanochannels of the ZIFHep membrane afforded a rapid and selective transport of Li+ over counteranions and other alkali ions due to electrostatic repulsion and optimal transport kinetics of cation-sulfonate ion pairs. A salinity gradient power generator (SGPG) was built by using the ZIFHep membrane as a cell separator coupled with a pair of Ag/AgCl porous membrane electrodes. At a salinity gradient of 105, such a power generator presented a significantly decreased internal resistance (25.6 Ω), three-order of magnitude lower than that reported previously, and an output power as high as 9.03 μW.