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.
Keywords: gradient polyelectrolyte membranes; ion transport; ionic diodes; osmotic energy generators; polysaccharides.
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