Engineered subnanochannel ionic diode membranes based on metal–organic frameworks for boosted lithium ion transport and osmotic energy conversion in organic solution

Harvesting Gibbs energy from a salinity gradient of waste organic solutions can not only alleviate the environmental pollution but also provide new energy resources to mitigate the energy shortage. However, the membranes with high ion selectivity, excellent ionic flux, and high-performance power output in organic solutions remain considerably unexplored. Here, we report on the metal–organic framework (MOF) based subnanochannel ionic diode membrane (IDM), comprising a large-area and continuous zeolitic imidazolate framework-8/polystyrene sulfonate membrane and a highly ordered alumina nanochannel membrane, for highly efficient osmotic energy conversion in organic solution. We show that a distinctly asymmetric design of pore sizes, charges, and wettabilities and the numerous highly negatively charged and angstrom-scale window-cavity pore structures in the MOF layer endow the subnanochannel IDM with directional and amplified Li+ ion transport and enhanced selectivity in methanol. Thus, an unprecedented power density of ∼23.4 W/m2 is achieved when a 2 M LiCl-methanol solution is mixed with the pure methanol, 5-times more than the existing value. This work provides significant insights into the use of rectified ion channel-mimetic membranes for achieving ultrafast Li+ ion transport at the confinement and high-performance energy harvesting from organic solutions.