Preparation And Osmotic Energy Conversion Of Gradient Polyelectrolyte Hydrogel Membranes

As a renewable and sustainable energy,the osmotic energy generated during the mixing of seawater and fresh water has drawn tremendous attention.With the development of nanotechnology and membrane science,researchers have increasingly focused on the development of ion exchange membranes for osmotic energy conversion.Asymmetric ion membranes composed of two different porous membranes have shown great advantages in harvesting osmotic energy.At present,the main problems of asymmetric membranes are interface incompatibility and low ion transport efficiency,resulting poor power density and durability.As a typical three-dimensional material with abundant ion channels and low ion transport resistance,hydrogel has several advantages of extensive applicable materials,easy large-scale preparation and anti-pollution.With these characters,hydrogel could be used to nanofluid systems.Herein,two asymmetric hydrogel membranes with continuous gradient structure have been prepared,which optimized the design of ion transport membranes from the structure,explored commercial application from the mechanism,and achieved highperformance osmotic energy generation.The main research results are listed as follows:1.All-polysaccharide polyelectrolyte hydrogel membranes with continuous gradient structure was prepared by ultrafast reaction-diffusion method,using natural polysaccharide such as chitosan and sodium alginate.Based on the electrostatic complexation of polyelectrolyte and the formation of hydrogen bond,the membranes have high tensile strength(~0.7 MPa)and ideal anti-swelling property.The continuous gradient structure also overcomes the unfavorable interface problems.It has been confirmed that CS/SA gradient polyelectrolyte membranes could achieve efficient osmotic energy conversion,due to high ionic conductivity,excellent cation selectivity and diode effect which promotes unidirectional ion transport in the membrane.The gradient polyelectrolyte hydrogel membrane-based devices present ultrahigh power densities of 7.87 W/m2 by mixing seawater and river water,superior to previously reported ones.More importantly,this study provides the first mechanistic explanation for the decrease of power density with the increase of test area and optimizes the RED device in experiment,which provides guidance for the development of ideal RED membrane-based power generation system.2.To exploit ion transport membranes with higher energy conversion performance,we have prepared gradient double network hydrogel by UV-initiated radical polymerization,using sodium 2-acrylamide-2-methylpropyl sulfonate(AMPS-Na)and agar.The cross-linking network of PAMPS and agar physical cross-linking network provide full negative charge and mechanical support respectively.Gradient PAMPS/Agar double network hydrogel membranes have ideal swelling resistance and high mechanical properties(0.4 MPa).In addition,the membranes have excellent ionic conductivity and diode effect(the rectification ratio is 3.62),thus achieving a superior output power density(12.2 W/m2)when applied to osmotic energy generation.PAMPS/Agar hydrogel membrane-based energy generation device shows excellent power generation performance and promotes the development and application of polyelectrolyte hydrogels in the field of osmotic energy generation.