Effect Of Divalent Ions On Electrochemical Properties Of Ion Exchange Membrane And Reverse Electrodialysis

Under the background of energy transformation,reverse electrodialysis as a new green renewable energy technology has attracted wide attention.Reverse electrodialysis converts the difference in salt energy into electricity by mixing water with two different salt concentrations.However,it has been found that when the actual water is used as the feed solution instead of sodium chloride solution,the power generation efficiency of reverse electrodialysis will decrease to a large extent in recent years.Compared with sodium chloride solution,the actual water is more complex in composition.Besides sodium ion and chloride ion,it also contains various high-priced ions.Ion exchange membrane as the core component of reverse electrodialysis,its performance directly affect the production performance of reverse electrodialysis,this thesis first respectively in the total concentration and total ionic strength invariant conditions,change the proportion of divalent ions in solution,different composition of electrolyte solution is studied the influence of the electrochemical properties of ion exchange membrane;Studies show that the presence of Mg²⁺will significantly increase the resistance of CEM film itself,while the presence of SO₄^2-will increase the resistance of AEM film itself,but the increase effect is not as significant as that of Mg²⁺for CEM,and the influence effect is further intensified with the increase of the proportion of divalent ions.Then,the influence of operating conditions?temperature and flow rate?of electrolyte solution on the electrochemical characteristics of the membrane itself and its interface layer was further investigated.The results showed that the flow rate of electrolyte solution did not affect the resistance value of the membrane itself,but increased flow rate would significantly reduce the resistance and capacitance of the diffusion boundary layer.Changing the temperature will reduce the resistance of the membrane and its interfacial layer due to the change of the ion migration rate in solution and the ion transfer function of the fixed-charge groups within the membrane,but changing the temperature has no significant impact on the interfacial layer capacitance of the ion-exchange membrane.Using mixed solutions of divalent ions with different compositions and NaCl as operating solutions,the effects of different divalent ions on the electrochemical characteristics of cathode and cation exchange membrane were investigated.Then,RED electrogeneration experiment was carried out on this basis to investigate the effects of different divalent ions on the resistance of RED device and the efficiency of RED electrogeneration.The ohmic and non-ohmic resistances of RED device were characterized by electrochemical impedance spectroscopy.Studies have shown that both Ca²⁺and Mg²⁺can increase the membrane resistance and interface resistance of cationic exchange membrane,and the increase effect caused by Ca²⁺on the membrane resistance and dual-layer resistance is greater than that of Mg²⁺,but the effect on the diffusion boundary layer resistance of Ca²⁺is smaller than that of Mg²⁺.SO₄^2-increases the membrane resistance of anion exchange membrane and its interface resistance.The influence of divalent ions on the interface layer of ion-exchange membrane is also related to the content of divalent ions in solution.The higher the proportion of divalent ions is,the more obvious the effect is.The results of electricity generation experiment show that under the premise of constant total ion strength,divalent ions will reduce the OCV of RED device,and the order of influence is SO₄^2->Ca²⁺>Mg²⁺.Divalent ions will increase the internal resistance of RED device.The order of influence is Mg²⁺>Ca²⁺>SO₄^2-.The order of influence on the maximum power density Pd of the device is Mg²⁺>Ca²⁺>SO₄^2-.However,as the content of divalent ions increases,the influence of divalent ions on Pd gradually approaches.This paper examines the external operating conditions?thick thin side solution salinity,thick thin side of the solution of velocity?influence on RED device production performance,the study found that the strong side of dilute solution salinity and flow rate are larger influence on production performance of reverse electrodialysis device,and through the experiment to get the best operating conditions:the concentration of a solution of thick thin side the proportion is appropriate,strong lateral velocity for dilute velocities of 0.8 times.