Anti-swelling Hydrogel-based Ion-selective Membrane For Osmotic Energy Conversion

The development of modern society and economic prosperity depend on energy.However,the large consumption of non-renewable fossil fuels has led to concerns about energy shortage and ecological pollution all over the world.Therefore,the development of clean and sustainable energy is one of the most important topics in recent years.The osmotic energy contained in the salinity gradient between rivers and oceans is abundant and widely distributed in theory,which has become a research hotspot.The membrane-based reverse electroosmosis is an effective method to collect osmotic energy,but the existing ion selective membranes are often hampered by high internal resistance or low selectivity.Therefore,it is urgent to break the balance between selectivity and permeability and construct excellent ion selective membranes.Polyelectrolyte hydrogels with low resistance characteristics are ideal materials for membrane-based osmotic energy collection.Typical polyelectrolyte sodium polyacrylate gel is a common ion exchange resin material,which contains a large number of hydrophilic carboxyl functional groups,showing good ion selectivity.In this paper,we choose a typical sodium polyacrylate（PAAS）hydrogel as the basis,and propose the concept of physically confined strategy to swelling resistance.With the natural balsa as the frame,a new hydrogel-based ion selective membrane with high stability and anti-swelling was successfully constructed.Firstly,sodium polyacrylate precursor solution was filled in the lined vessel channels of natural balsa wood under vacuum conditions,and wood hydrogel composite membrane was obtained by polymerization.Through the optimization of conditions,the composite membrane with the best performance was prepared.The material morphology,functional group characterization,mechanical properties and so on proved the successful construction of composite membrane.The morphology,structure,thermodynamic and electrochemical stability of the membrane were tested to prove the feasibility of the anti-swelling strategy,and this strategy also has scalability.The prepared wood hydrogel film can achieve high performance energy conversion with salinity gradient.Under the artificial simulated sea/river interface environment（50-fold Na Cl salinity gradient）,the film has high ion selectivity which can be up to 0.857,the corresponding energy conversion efficiency is 25.5%.And the maximum output power density is up to 8.5 W m^-2,much higher than the commercial membrane reference(5 W m^-2),and higher than most reported ion-selective membranes.The maximum output power density can reach 10.6 W m^-2under real river/seawater conditions.This work provides effective guidance for the design of low cost,environmental protection and high-performance hydrogel-based ion selective membranes.