Research On Mechanical And Conductive Properties Of Cellulose-Based Ion Exchange Membrane For Fuel Cells

Nowadays,due to the shortage of non-renewable energy such as oil,natural gas and coal,it has become the consensus of all countries in the world to develop new energy.As a clean,efficient and sustainable new energy,hydrogen can give full play to its advantages of high energy density,zero pollution and zero carbon emission when applied to fuel cell technology,which is helpful to solve the problems of energy crisis and environmental pollution.The ion exchange membrane is one of the key components of fuel cells.However,most of the existing commercial ion exchange membranes are prepared based on synthetic polymers,which have complicated synthesis process and high production cost.At the same time,it is easy to cause environmental pollution because it is difficult to degrade.These shortcomings hinder their further development and application.Therefore,in this thesis,cellulose,a natural macromolecular material,was selected as the membrane matrix,conductive units were introduced by blending,dyeing and in-situ polymerization,and the microstructure in the membrane was adjusted by cross-linking and interpenetrating,and a series of green and high-performance ion exchange membranes were developed.The main research contents are as follows:（1）Using viscose cellulose as the membrane matrix,the basement membranes（PVMs）was prepared by casting,coagulating,stretching and freeze-drying steps.Then,the membranes were cationically modified with glycidyl trimethyl ammonium chloride solution（GTA）,and the reactive dye KE-7B1 was grafted onto the basement membranes by dyeing technology,and a series of dyed viscose-based proton exchange membranes（DVM）were obtained.The analysis of FT-IR,SEM and XPS demonstrates that KE-7B1is successfully introduced into the viscose basement membranes.The H⁺conductivity of DVM-15 is the highest,which is 14.31 m S cm^-1 at room temperature and 44.19 m S cm^-1at 80 ^oC.The results of methanol permeability test show that the methanol permeability of DVM-15 is 1.09×10^-7 cm² s^-1,which indicates that DVM-15 has good alcohol resistance.AFM analysis indicates that DVM-15 has more continuous hydrophilic channels than PVM,which is beneficial to improve the proton conductivity of the membrane.With the support and reinforcement of polyvinyl alcohol（PVA）,the maximum breaking strength of PDVM membrane reachs 42.12 MPa.Simultaneously,the weight loss rate of PVM and DVM-15 is less than 10%after 120 h under the strong oxidation condition of 30 wt%hydrogen peroxide,showing good oxidation resistance.The single cell power generation test shows that the peak power density of DVM-15 reaches 62.96m W cm^-2 at 179.89 m A cm^-2,which is much higher than that of unmodified PVM(6.11m W cm^-2).（2）Using bacterial cellulose（BC）with high porosity as membrane matrix,a series of anion exchange composite membranes were prepared by introducing polydimethyl diallyl ammonium chloride（PDDA）into BC membrane through in-situ polymerization.Among them,BC-PDDA-45 shows excellent OH^-conductivity,which is 64.37 m S cm^-1at room temperature and 112.14 m S cm^-1 at 80 ^oC.FT-IR and XPS analyses indicate that DDA is successfully polymerized in situ in the membrane,and forms various forces with cellulose macromolecular chains,and it can stably reside in BC membrane.SEM images show that with the increase of polymerization degree of PDDA,the entanglement of macromolecules increases and the interior of the membrane becomes denser.The analysis of water contact angle shows that the hydrophilicity of the surface of the prepared anion exchange membrane decreases with the increase of PDDA polymerization degree,which effectively controls the water content in the membrane and is beneficial to the hopping transmission of ions.The analysis of water contact angle shows that the surface of anion exchange membrane is hydrophilic,which is beneficial to ion transmission.Thermogravimetric analysis indicates that BC-PDDA-45 has good thermal stability,and its maximum degradation temperature is 278 ^oC.The oxidation stability of the membranes is tested under the strong oxidation condition of 30 wt%hydrogen peroxide.The results indicate that the weight of the membrane remains above 80%after soaking for 120 h,which shows good oxidation resistance.The results of mechanical properties analysis show that PDDA can effectively improve the elongation at break and flexibility of BC membrane.（3）Using bacterial cellulose as the substrate,reactive dye KE-7B1 with sulfonic acid groups was introduced to construct an efficient three-dimensional proton transport channel to improve the proton conductivity of membranes.Before dying,cationic modification was carried out by DDA in-situ polymerization to reduce the electrostatic repulsion between cellulose anion and dye anion in the dyeing process,and thus improve the dye uptake.The chemical structure test results of the membranes demonstrate that KE-7B1 is successfully introduced into the bacterial cellulose membrane.The conductivity of DBC-PDDA-30 membrane reaches 25.26 m S cm^-1 at room temperature and 54.96 m S cm^-1 at 80 ^oC,which indicates that the porous structure of bacterial cellulose is conducive to graft more ionic conductive groups than viscose membrane.The results of thermogravimetric analysis show that DBC-PDDA series membranes have good stability within 200 ^oC and meet the temperature requirements in practical application.The membranes possess good mechanical properties,in which the breaking strength of DBC-PDDA-30 membrane reaches 31.45 MPa and the breaking elongation rate is 6%.The peak power density of the single cell assembled with DBC-PDDA-30 membrane reaches 107.46 m W cm^-2 at 209.13 m A cm^-2.