Mesoscale Simulation On Hydration Morphology Of Proton Exchange Membrane

Protort exchange membrane fuel cell,a power source of high conversion efficiency and zero-emission,is thought will play an important role in global carbon neutralization and the future development of society.As the core of the fuel cell,the transport of protons takes place here.The non-enough understanding of the morphology and mechanism of proton transport in the proton exchange membrane slows down the improvement of the membrane performance.Proton transport in proton exchange membranes with hydrophobic main chain and hydrophilic side chain usually depends on the proton transport channels composed of hydrophilic and hydrophobic phases.In this paper,the effects of the chemical structure of the main side chain,the hydrophilic group of the side chain,constructing the polyacid side chain or multiple proton binding sites by doping small molecule acids,and using a new sulfonated aromatic backbone polymer on the hydration morphology of proton exchange membrane were studied.Dissipative particle dynamics were used.Three kinds of perfluorosulfonic acid membranes with different main and side chain lengths Nafion,Dow and Aciplex were considered at first.With the increase of water content,the simulated morphology changes from isolated water clusters to interconnected water channels.However,the simulated morphology is different for three membranes,and Nafion appears to show wide and continuous hydrophilic channels.The increase of equivalent weight leads to the decrease of water cluster size and higher water dispersion;this is related to the high crystallinity of the long main chain.After that,the hydration morphologies of ionomers with sulfonic acid,phosphoric acid,methylphosphoric acid,carboxylic acid and imidazole functionalized alkyl as side chain termination groups were studied,and the water diffusion was approximately expressed as well.Among them,phosphoric acid terminated ionomer ? showed similar cluster size and faster water diffusion than ionomer ?,while methyl phosphoric acid terminated ionomer ? and imidazole functionalized alkyl terminated ionomer ? showed small cluster size than?,However,both of them can keep fast water diffusion under low water content.The carboxylic terminated ionomer ? has little dependence on the water content,and can maintain a larger cluster size and water diffusion rate even at low water content.In the study on the hydration morphology of poly acid side chain ionomers,two sulfonic acid groups lead to the increase of proton binding sites and the dispersed distribution of water in the membrane,which leads to smaller cluster size and faster water diffusion.In addition,we also prepared several acidic groups system by blending the sulfonic acid modified silica.The cluster size of the blend membrane is similar to that of Nation,and the water diffusion velocity is high.For sulfonated polyether ether ketone,with the increase of sulfonation degree at low water content,the size of water clusters increases,but the change is not obvious.In addition,by adding polyethersulfone to construct the hydrophilic and hydrophobic difference under the intermolecular,we obtained the composite membrane with large cluster size.The author hopes that the research work in this paper can be used for reference in the development of new proton exchange membrane.