Study On Modification Of Sulfonated PVDF Cation Exchange Membrane And Salt Differential Power Generation Performance

Salt differential energy is a kind of green and clean energy stored in seawater.Reverse electrodialysis salt differential power generation（RED）is an effective way to extract salt differential energy.Moreover,red technology has the advantages of no pollution to the environment,green environmental protection,wide energy storage range,high energy density and long-time operation.Ion exchange membrane is the core of RED technology.The preparation of ion exchange membrane dedicated to RED power generation needs to reduce the resistance and improve the selective permeability and ion flux.In order to prepare such ion exchange membrane,this paper uses PVDF cation exchange membrane doped with inorganic particles to explore the physicochemical properties of the modified cation exchange membrane,and discusses the influence of the modified PVDF cation membrane on RED power generation performance compared with commercial cation exchange membranes.In this paper,PVDF is used as the base membrane material,and the technical route is"base membrane→alkalization→grafting→sulfonation".Styrene is grafted onto PVDF base membrane,and then sulfonated to connect sulfonate to the ion exchange membrane to obtain PVDF sulfonated cation exchange membrane.The physical,chemical and electrochemical properties of ion exchange membrane were investigated by electron microscope（SEM）,Fourier infrared spectrometer（FTIR）,electrochemical workstation and other membrane performance test methods.The water content of PVDF sulfonated cation exchange membrane is 30.3%,the contact angle is 74°,the selective permeability is 90%,the resistivity is 15.8Ω·cm^-2and the ion conductivity is1.5×10^-3S·cm^-2,and the ion exchange capacity is 1.7 m M·g^-1.At the same time,the composite modified ion exchange membrane with silica and mesoporous silica was prepared by doping modification on the basis of PVDF base membrane.With the addition of silica particles,the surface morphology of the ion exchange membrane is changed,the hydrophilicity of PVDF membrane is effectively improved,and its moisture content and contact angle are significantly improved.The ionic conductivity of the modified ion exchange membrane is also improved to a certain extent.The experimental results show that the optimum addition of Si O₂in PVDF/Si O₂sulfonated cationic membrane is 1.5%.At this time,the moisture content of the membrane is 40.8%,the contact angle is 56°,the selective permeability is 86%,the resistivity is 14.1Ω·cm^-2and the ion conductivity is1.7×10^-3S·cm^-2,ion exchange capacity is 2.1 m M·g^-1.By adding mesoporous silica（m Si O₂）,the internal structure of PVDF membrane is improved by taking advantage of the high specific surface area of particles and the characteristics of internal pores.At the same time,the performance of PVDF/m Si O₂sulfonated cationic membrane is improved.The experiment shows that the optimal addition amount of m Si O₂is 1.5%,At this time,the moisture content of the membrane is 43.1%,the resistance is 13.9Ω·cm^-2and the ion conductivity is 1.7×10^-3S·cm^-2,and the ion exchange capacity is 2.2 m M·g^-1.In order to explore the influence of the pore size of the added material on the PVDF sulfonated cation exchange membrane,the microporous material molecular sieve powder was used for composite modification.The experiment showed that the optimal amount of molecular sieve in the PVDF/molecular sieve sulfonated cation membrane was 1%,the moisture content of the membrane was 45.8%,the resistance was 11.4Ω·cm^-2and the ion conductivity was 2.17×10^-3S·cm^-2,ion exchange capacity is 2.5 m M·g^-1.Then,the commercial cation exchange membrane is used to explore the influencing factors of RED power generation process through conditional experiments,and the power generation performance of commercial cation exchange membrane under the best conditions is obtained.In RED power generation equipment,when the diaphragm thickness is 0.8 mm and the water supply flow rate is 100 ml·min^-1,the breaking voltage of commercial ion exchange membrane is 98 m V,the short-circuit current is 3.5 m A,and the maximum power generation is 0.87 W·m^-2.Finally,the prepared PVDF ion exchange membrane and modified ion exchange membrane are applied to RED power generation equipment,and the power generation performance is compared with that of commercial cation exchange membrane under the best power generation conditions.The experimental results show that the maximum RED power of PVDF sulfonated cation exchange membrane is 0.57 W·m^-2;The optimum addition of Si O₂in PVDF/Si O₂composite ion exchange membrane is 1.5%,and the maximum RED power is 0.79 W·m^-2;The optimum addition of m Si O₂in PVDF/m Si O₂composite ion exchange membrane is 1.5%,and the maximum RED power is0.87 W·m^-2;The optimum addition of molecular sieve in PVDF/molecular sieve composite ion exchange membrane is 1%,and the maximum RED power generation is 1.05 W·m^-2,which is 20%higher than that of commercial cation membrane.