Preparation Of Novel Tetramethoxy Side Chain Difluoromonomers And Fuel Cell Cell Performance Test

Proton exchange membrane fuel cells are a type of electrochemical energy converters which can convert directly the chemical energy of fuels into electric energy.With hydrogen and oxygen used in proton exchange membrane fuel cells,the only by-product of proton exchange membrane fuel cell is water.Besides,proton exchange membrane fuel cells exhibit the wide-range power,low operating temperature,high efficiency,high power density and a long service life.Generally,proton exchange membrane plays an important role in the development of proton exchange membrane fuel cells.The research on proton exchange membranes is mainly focused on the preparation and performance of sulfonated poly(ether ketone)and sulfonated poly(ether sulfone).However,proton exchange membranes also have some drawbacks,such as poor dimensional stability under the condition of highly sulfonated degree and low chemical stabilities.Up to now,many ionomers have been developed to improve the stabilities of the proton exchange membranes.Here,two novel difluoro monomers containing side-chain and cross-linkable groups are developed,and the corresponding membranes are obtaine,meanwhile the properties of the membranes are investigated.The details of this research are as follow:(1)The intermediate TBDFED was prepared with 1-(2,6difluoro phenyl)-2-(3,5-dimethoxy phenyl)ethane-1,2-dione(DFDMED)by bromination reaction.The monomer,TBDFTMED,is prepared via Suzuki cross-coupling reaction with 3,5-dimethoxy phenyboronic acid and TBDFED.All the compounds are confirmed by infrared(IR),proton nuclear magnetic resonance(1H-NMR)and gas chromatography with electron impact-mass spectrometry(GC-MS),respectively.Poly(arylene ether sulfone)s including multiple methoxypheny are synthesized via polycondensation reaction of 4,4’-biphenol(BP),4,4’-difluorodiphenyl sulfone(DFDPS)and TBDFTMED.Unfortunately,the viscosity of the prepared polymers is too low to prepare a tough membranes,the following investigation is ongoing.(2)Using 4-Methoxybenzylchloride and 2,6-difluorobenzonitrile,as starting materials,compound DFMED was prepared by Grignard reaction,nucleophilic addition reaction,hydrolysis reaction and oxidizing reaction.Intermediate DFOED is obtgained via demethylation of DFMED.Through bromination reaction between DFOED and N-Bromosuccinimide,bronmiated intermediate DBODFED was prepared.Then the diflouor monomer was prepared via Suzuki cross-coupling reaction with 3,5-dimethoxypheny boronie acid and DBODFED.The overall yield is 20%.The structures of the monomer and intermediates were confirmed by infrared(IR),proton nuclear magnetic resonance(1H-NMR)and gas chromatography with electron impact-mass spectrometry(GC-MS).(3)The synthetic conditions of AODFMED was improved,where the intermediate DBMDFED was synthesized by methylation of DBODFED using dimethyl sulfate,and the monomer CH3-AODFMED was prepared via Suzuki coupling reaction between 3,5-dimethoxypheny boronic acid and DBMDFED.CH3-AODFMED-based poly(arylene ether sulfone)s(PAES-OMe)bearing multiple pendant methoxyphenyl groups are synthesized via poly condensation reaction of 4,4’-biphenol(BP),4,4’-difluorodiphenyl sulfone(DFDPS)and CH3-AODFMED.Sulfonated poly(arylene ether sulfone)s ionomer r-SPAES was obtained via demethylation of PAES-OMe using boron tribromide and followed by nucleophilic substitution using 1,4-butane sultone.Finally,proton exchange membrane was prepared and its properties were investigated.(4)Nafion 212 membrane is employed as the basic membrane;hot-pressing process of membrane electrode assembly(MEAs)is optimized and the performance of single cell is tested with the hydrogen as fuel and pure oxygen as oxidant.Compared with the former studies,the operating conditions of fuel cells are optimized.The results show that the maximum power density of Nafion 212 membrane electrode assembly is 534.00 mW/cm2,which is comparable to the reported one.The MEA with membranes B-SPAES(5/5)and SPAES(1/2)was prepared and the performances of single cell were tested.The results show that the cell performances of B-SPAES(5/5)membrance is superisr to SPAES(1/2)membrance inspite of their similar IECs and conductivities.