Preparation And Properties Of Cellulose-based Nanofiber Composite Proton Exchange Membranes

Proton Proton exchange membrane fuel cell(PEMFC)has become a fast developing and widely used fuel cell due to its characteristics and advantages of high energy density,low noise,low working temperature and environmental friendliness.The dense proton exchange membrane(PEM)is a key component in the fuel cell system,and this membrane can play the role of isolation gas,insulating electrons and exhibiting high proton conductivities as proton carrier from the anode to the cathode.Nafion(?),which is a series of perfluorosulfonic acid membranes,has numerous drawbacks,such as high methanol permeability,low thermal stability,and critical proton conductivity reduction at high temperatures,which hinder its widespread application.Hydrocarbon backbone polymers have advantages of low cost,good physical and chemical properties,which they are easier to be sulfonated and modified.However,the highly sulfonated degree,these polymers have a certain gap,severe swelling,poor mechanical properties and when sulfonated degree is low,the proton conductivity reduced.Constructing continuous proton conducting channels and adding hydrophilic materials in PEMs are effective methods to increase their proton conductivity.In recent years,it has become a research hotspot to construct proton conducting channels by inserting nanofibers into membranes.In this paper,solution-blown cellulose nanofibers were expected to improve proton conductivity of PEM by being integrated in the sulfonated poly(ether sulfone)(SPES)matrix,the main contents are as follows:We first prepared CA nanofibers by electrostatic-induction-assisted solution blow spinning(EISBS),and cellulose nanofibers were then obtained through hydrolytic treatment in NaOH/EtOH solution.Then,SPES/Cell membranes with different contents of cellulose nanofibers were prepared by solution impregnation.The structure,morphology and properties of cellulose nanofibers and membrane were studied.The diameters of CA nanofibers are mainly ranged in 150nm-1000nm,while that of cellulose nanofibers ranged in 200-800 nm,the nanofibers are smooth and uniform.The composite membrane has good proton conductivity,hydrophilicity,thermal stability,mechanical strength and methanol permeability.Due to the addition of cellulose nanofibers with water retention properties,the hydrophilicity of the composite membrane was improved and proton conducting channels were also constructed.The proton conductivity of the SPES/Cell membrane reached 0.13S/cm when the content of Cellulose nanofibers is 5%at 80 ?,100 RH,which increased by 1.6 times compared with pure SPES membrane.The paper further incorporates phosphorylated cellulose nanofibers into the SPES matrix to prepared P-Cell/SPES composite membrane,its structure and performance studies have shown.Phosphate groups can provide more proton transfer sites in the membrane.The water absorption of P-Cell/SPES-0.25M composite membranes is 1.22 times higher than that of SPES/Cell membranes at 40? after the introduction of phosphoric acid groups,which improved the thermal stability of P-Cell/SPES composite membranes.P-Cell/SPES-0.25M composite membrane has the highest proton conductivity up to 0.154S/cm.We use that the imidazole heterocyclic structure can provide proton donors(N-H)and proton acceptors(N:),imidazole molecules and sulfonic acid groups of SPES can form acid-base pairs to improve the proton exchange membrane conductivity.The SPES/Cell/Im composite membranes were prepared by solution impregnation.The thermal stability,mechanical behavior and methanol permeation of the composite membranes were improved,the proton conductivity of the SPES/Cell/Im-30 composite membrane can reach 0.123 S/cm(80??100 RH).