Anti‐Swelling Gradient Polyelectrolyte Hydrogel Membranes as High‐Performance Osmotic Energy Generators

Emerging asymmetric ionic membranes consisting of two different porous membranes show great superiority in harvesting clean and renewable osmotic energy. The main barriers constraining their applications are incompatible interfaces and a low interfacial ionic transport efficiency, which are detrimental to the long‐term stability and improvement of the power density. Here, continuous‐gradient all‐polysaccharide polyelectrolyte hydrogel membranes prepared by ultrafast reaction/diffusion have been demonstrated to enable high‐performance osmotic energy conversion. Besides an inherent high ion conductivity and excellent ion selectivity, the anti‐swelling polyelectrolyte gradient membranes preserve the ionic diode effect of the asymmetric membranes to facilitate one‐way ion diffusion but circumvent adverse interfacial effects. In consequence, they can present ultrahigh power densities of 7.87 W m −2 by mixing seawater and river water, far superior to state‐of‐the‐art membranes.