Preparation And Performance Analysis Of Alkaline Polymer Electrolyte For Fuel Cell

With the rapid development of the global economy,the world economy has achieved rapid growth,and at the same time the use of energy on the earth has also greatly increased.The contradiction between the rapid consumption of traditional fossil energy and the ever-increasing energy demand of human society has become more and more prominent,and people’s needs for environmentally friendly and renewable new energy are becoming more and more urgent.The polymer electrolyte membrane fuel cell is considered by researchers as a feasible technical method to solve the problem of energy shortage and environmental pollution because of its high specific power,high energy conversion efficiency,renewability and environmental friendliness.Anion exchange membrane fuel cells have attracted more and more attention from scholars due to their advantages such as better redox kinetics,less fuel permeation and the use of non-precious metal catalysts.However,as the core component of alkaline fuel cells,AEMs still have problems such as low conductivity and poor alkali resistance.To solve the above problems,the ion conductivity of the membrane can be directly improved by increasing the ion exchange capacity（IEC）of the membrane,but it will inevitably lead to problems such as poor dimensional stability and weakened mechanical properties.In addition to improving the IEC of the membrane,the overall performance of the membrane can be fundamentally improved by changing the structure of the membrane.Metal-organic frameworks（MOFs）,as a kind of porous nanomaterials,are inorganic-organic hybrid materials synthesized through the self-assembly of metal ions and organic ligands to form coordination bonds.Because of its large specific surface area,active sites,controllable and adjustable features,it has been widely studied and applied.Therefore,this paper designed to use phytic acid to synthesize MOFs and polymer backbone to prepare anion exchange membranes.Through systematic characterization and testing,the relationship between different membrane structures and properties was explored in detail.The main work is as follows:In the first series of membranes,under the action of glutaraldehyde（GA）crosslinking agent,the polyhydroxy compound phytic acid（PA）is compounded in polyvinyl alcohol（PVA）,and octadecylamine（ODA）is introduced at the same time.ODA is grafted onto the polymer backbone as a hydrophobic group.Through FT-IR spectroscopy,scanning electron microscopy（SEM）and thermogravimetric analysis（TGA）,the chemical structure and properties of the synthetic composite film（PA/GA_X-PVA）were analyzed.At the same time,systematically test the relative performance of the synthetic product membrane.The results show that the composite membrane with lower crosslinker content can expose more hydroxyl groups and chelate more metal ions to increase the conductivity of the membrane,but the composite membrane with lower crosslinker content has a higher swelling degree.At 80 o C,the OH^-conductivity range of PA/GA_X-PVA（X=0.10,0.15,0.20,0.25）is 1.92×10^-2S·cm^-1-1.25×10^-2S·cm^-1.In addition,the PA/GA_0.25-PVA film with a higher content of crosslinking agent still maintains a higher conductivity after being soaked in lye for 120 hours,and its value is about 90.77%of the initial conductivity.In order to increase the conductivity of the anion exchange membrane and reduce the swelling of the membrane,the second series of membranes is based on the in-situ introduction of a mixture of phytic acid（PA）,methanol,water and N,N-dimethylformamide（DMF）in polyvinyl alcohol casting membranes（Phytic acid and chromium nitrate nonahydrate form a metal organic frame structure with a three-dimensional structure）.At the same time,glutaraldehyde（GA）is used as a crosslinking agent to construct a series of anion conductive membranes（AEMFC）with porous metal organic framework（MOF）structure suitable for fuel cell.During the experiment,the structure oand physical and chemical properties of the membranes are optimized by adjusting the different mass percentages of Cr content in the composite membranes.The results show that the composite membranes are flat and uniform in appearance,and contain a large number of pore structures for OH^-migration and retention of water molecules.At the same time,membranes’conductivity,water uptakes,and mechanical properties increase with the increase of Cr mass fraction was increased.When the mass rati of m(Cr³⁺):m（MOF@PVA composite membrane）=1.2:100,the conductivity of the composite membrane is the highest,that is 24.88 m S·cm^-1.In addition,the composite membrane can still maintain good performance after alkali treatment in a 3 mol·L^-1Na OH solution sample bottle at 80 o C for 168 hours,and the conductivity is only reduced by 8%.