Preparation And Properties Of Nafion/sepiolite Ionogels Electrospun Composite Proton Exchange Membranes

The current proton exchange membrane fuel cells(PEMFC)based on commercial perfluorosulfonic acid resin membranes(such as Nafion)have many shortcomings,especially the battery operation is highly dependent on the liquid water environment,which leads to the complex water and heat management system of the battery and the actual energy efficiency of the battery far from reaching the theoretical value.In order to simplify the design of the PEMFC system and improve the energy efficiency of the system,using Nafion composite membranes with high proton conductivity in a low humidity environment is an effective strategy.In this paper,supercritical CO₂ was used to assist the preparation of ionic liquid-filled sepiolite(IL@SNR)as a new type of proton carriers,and the electrospinning process was used to prepare nanofiber composite membranes for PEMFC performance research to reduce the battery's dependence on harsh temperature and humidity environments.The specific research contents are as follows:Firstly,the supercritical CO₂ was assisted to prepare IL@SNR ionogels.The ionic liquid(IL,1-butyl-3-methylimidazole trifluoromethanesulfonate)was filled into the internal nano-pores of sepiolite nanorods(SNR)under the actions of Sc CO₂ with excellent dissolution and penetration ability.The FTIR,XRD,XPS,Raman,XPS,TEM and TG-DSC were emplored to characterize the structural characteristics of sepiolite before and after IL filling,the phase morphology characteristics of IL in the sepiolite pores,as well as calculate the amount of IL filling.The results showed that,the maximum amount(108%)of IL loading was achieved under the conditions of 12 MPa of the reaction pressure,60?of the reaction temperature,6 ml of the co-solvent ethanol and 6 h of the reaction time.Secondly,Nafion/IL@SNR composite membranes were prepared by solution casting method.Proton carriers such as IL@SNR,sulfonic acid groups on the Nafion molecular chain and water molecules in the composite membrane were acted to form a continuous path to conduct protons,so as to reduce the dependence on the free water in the membrane to conduct protons.By using FESEM,XRD,TGA and other characterization methods,and testing mechanical performance,water absorption,dimensional stability,proton conductivity and single cell performance,the analysis of the distribution of IL@SNR in composite membranes,the relationship between the structure and performance of the membranes were carried out.The results show that even distribution of IL@SNR ionogels in Nafion matrix can promote the regular arrangement of the molecular chains of the perfluorosulfonic acid polymer,so that the mechanical strength,thermal stability,dimensional stability as well as the water absorbability of the composite membranes were significantly improved.Thus,Nafion/IL@SNR composite membranes exhibited excellent proton conductivities and battery performance under low humidity in the temperature range of 20?80?.Additinally,the 0.05 S/cm of proton conductivity of Nafion/2.0IL@SNR composite membrane was achieved under 40%RH.Lastly,Nafion/IL@SNR electrospun composite membranes were prepared and characterized.With the action of the electric field,the the proton conduction channels inside electrospun composite membranes are to enhance the ordered connectivity,thereby improving the proton conduction performance.With the characterizaitons of FESEM,XRD,TGA and tests of mechanical properties,water absorption,dimensional stability,proton conductivity and single cell performance,the optimal processing conditions of electrospinning were determined.Due to the formation of"reservoir"in nanofibers,the water absorption and retension capacity were enhanced.It was found that,more than 0.08 S/cm of proton conductivities of the ES-Nafion/2.0IL@SNR composite membrane were reached with the conditions of 80?and 40%RH,which showed the potential application prospects for PEMFCs operated under low humidity.