The Influence Of Amino Functionalized Mesoporous Silica On Properties Of SPEEK/IL Composite Membrane

The medium temperature proton exchange membrane fuel cell(PEMFC)has high energy conversion efficiency,excellent CO tolerance and simplified hydrothermal management,and has become the current research hotspot.Proton Exchange Membrane(PEM)is a key component of PEMFC,which acts as a barrier to the cathode and anode and conducts protons.At present,most commercial PEM are Nafion membrane.Although its conductivity is high and its stability is good,the conduction is excessively dependent on water,which requires normal humidification to work properly,which makes water management difficult and expensive.At medium temperature,due to the evaporation of water,the proton transfer process in PEM will break down,which seriously affects the fuel cell efficiency and limits the application of PEMFC at medium temperature.Therefore,the development of PEM that can conduct protons under medium temperature and anhydrous conditions is one of the key issues for the wide application of PEMFC.As a room temperature molten salt,ionic liquid(IL)is a good alternative to water proton conductor because of its high electrical conductivity under medium temperature and anhydrous conditions,wide and stable electrochemical window and low saturated vapor pressure.In medium temperature PEM applications,IL can be added to a polymer,such as a sulfonated polyetheretherketone(SPEEK,SP)matrix to prepare a SPEEK/IL composite membrane that conducts protons at medium temperature and anhydrous conditions.SPEEK is easy to synthesize,inexpensive,and environmentally friendly,and has a similar structure to Nafion but better overall performance than Nafion.However,IL is liquid,soluble in water,easily lost,and the mechanical properties of such composite membranes are poor.Therefore,it is necessary to introduce a stable inorganic solid filler to carry IL,such as mesoporous silica(NMS),which can utilize its surface interaction to retain IL and improve the mechanical properties of the composite membrane.However,the study found that the proton conduction site is degraded by the non-conductivity of silica,which destroys the continuity of proton hopping,which leads to the decrease of proton conductivity of composite membrane with the increase of filler content.Further research has found that modifying the surface of silica can improve its proton conductivity.The main research contents and conclusions of this study are as follows:1)A continuous proton channel is constructed in the composite membrane based on the modified mesoporous silica.First,an amino functionalized mesoporous silica(AMS)was prepared and the amount of amino groups grafted on the mesoporous silica surface was optimized.The modified mesoporous silica was incorporated into the polymer SPEEK and IL to prepare an SP/IL/AMS composite membrane.The SEM results of the membrane cross-section show that the modified mesoporous silica is uniformly dispersed in the composite membrane,and a continuous channel is constructed,which reduces the proton jumping energy barrier and improves the proton conductivity.Under medium temperature and anhydrous conditions,the conductivity of the SP/IL/AMS composite membrane doped with AMS is about 4 times that of the SP/IL/NMS composite membrane doped with unmodified NMS;2)Based on imidazole IL(N-ethylimidazole trifluoromethanesulfonate,Elm[Tfo]),the channels of proton transfer are synergistically formed in the composite membrane without humidification.The structure of imidazole-IL consisting of bonsted acid(proton donor)and b(?)nsted base(proton acceptor)enables it to allow protons to jump directly from proton donors to proton acceptors.The SP/IL/AMS composite membranes for conducting protons under medium temperature and non-humidification conditions were prepared by self-assembly method.FT-IR results show that SPEEK,IL,and AMS are combined by intermolecular force and electrostatic force.The introduction of amino groups constitutes a continuous channel,and the introduction of IL promotes proton conduction of the composite membrane under non-humidified conditions;3)Based on the interaction between the amino group in AMS and the sulfonate in SPEEK,the dimensional stability and tensile strength of the composite membrane are improved.The swelling degree of all SP/IL/AMS composite membranes doped with AMS was lower than that of SP/IL/NMS composite membranes,and the SP/IL/3-AMS composite membrane with the highest amino content had the lowest expansion degree.This is due to the acid-base interaction between-NH2 of AMS and-SO3H in SPEEK,which reduces the swelling degree of the composite membrane and improves its dimensional stability;4)The DMA results and TG results of the composite membrane showed that the introduction of NMS and AMS improved the mechanical properties and thermal stability of the composite membrane,and all composite membranes were stable at 270℃.The above results indicate that the composite membrane prepared in this paper is a potential candidate for application in PEMFC under medium temperature and non-humidification conditions.