Preparation And Properties Of Proton Conductivity Exchange Membranes Based On Polynorbornenes With Bifunctional Groups

Proton exchange membrane fuel cell(PEMFC)is a kind of power generation device which transforms chemical energy into electric energy by electrochemical reaction.It has developed rapidly because of varieties of merits,such as high energy conversion efficiency,low emission and quick start-up.In addition these,PEMFC can also work consistently in poor condition especially in the areas of electronic cars,power plant and portable power source.Proton exchange membrane is one of the key component in PEMFC.There are two main function for membranes.One is preventing fuel crossover,and the other is transporting protons from anode to cathode to ensure the successful reaction.Nowadays,The most widely used membranes are the Nafion series as the representative of the direct chain of all fluorine sulfonic acid proton exchange membrane.Although Nafion series have comprehensive performance,there are also some shortcomings such as fuel penetration and high cost and so on.In order to solve those problems,the semi fluorinated and non-fluorinated proton exchange membrane were studied and developed.Additionally,crosslinking structure was introduced into membranes to increase the mechanical performance and chemical stability.This paper reported a novel proton exchange membrane based on norbornene derivatives with sulfonate-carboxylate bifunctional groups.The molecular dynamics simulation was used to confirm the feasibility of this new structure via Materials Studio.The mean square displacement and radial distribution function of molecular chain are obtained by calculating and analyzing the trajectory of micro particles in proton exchange membranes.The diffusion coefficient of protons and water molecules were calculated with the formulas.In addition,proton conductivities were calculated based on the results.At298K,the proton conductivity of the membrane is 46.14mS/cm,which met the requirement for fuel cells and meant that the bifunctional norbornene structure is feasible.By setting different structural units,the influence of different ionizing degree of the carboxylic on proton exchange membranes was analyzed.The results showed that with the increasing ionizing degree of carboxylic acid,the proton conductivities tended to rise.Based on the analysis of the prediction of molecular dynamics,a novel random copolymer of 4-(bicyclo[2.2.1]hept-5-en-2-yl)benzene-1-sulfonylchloride(NBSC)and dimethyl 8,9,10-trinorborn-5-ene-2,3-dicarboxylate(DCNM),via ROMP reaction,cross-linked by dicyclopentadiene(DCPD)was proposed.Reactional conditions were explore by using the orthogonal experimental method,such as feed ratio,temperature,catalyst content and reaction time according to polymer molecular weight and molecular weight distribution.The optimal experimental conditions was 40~45~oC,30min.etc.A series of proton exchange membranes were obtained by changing crosslinking agent dosage.After alkali washed,pickled and immersion in deionized water,bifunctional proton exchange membranes with sulfonic acid and carboxylic acid were obtained.The structures of monomers and polymers were verified by nuclear magnetic resonance ~1H spectroscopy and Fourier transform infrared spectroscopy.The proton exchange membranes were tested.The results demonstrated that the decomposing temperature of the functional groups in proton exchange membranes was250~oC,the main chain decomposing temperature was 400~oC.With the increasing content of DCPD,swelling rate and water absorption decreased and the tensile strength increased gradually.The highest tensile strength was 20.15MPa at 25~oC,while the proton conductivity was up to 123.96 mS/cm.With comprehensive consideration,H02 and H03films was selected to prepare membrane electrode(MEA)by using the catalyst spray diffusion layer(GDE)method.At 60~oC,the gas flow was 60ml/min,catalyst loading was1mg/cm2,the open circuit voltage of the membrane electrode H02 film was 0.92V,and the maximum power was 68mW/cm~2.