Preparation And Characterization Of Ldh Doping Speek Composite Proton Exchange Membranes

Proton exchange membrane fuel cell(PEMFC), which has high energy conversion efficiency, high power density, low operation temperature and start-up quickly, is considered to be the most promising energy conversion device. Among them, the proton exchange membrane is the core component of direct methanol fuel cell and the most popular membranes are Nafion® membranes from the United States Dupont currently, which has been widely applied. However it has some significant drawbacks,such as high methanol permeability. Therefore the study of DMFC should focus on developing a low-cost and high-performance membrane, which can alternative Nafion membrane.Poly(ether ether ketone) is a kind of low cost and good performance of poly aryl ether ketone polymer. After sulfonated PEEK, we can get SPEEK. SPEEK membraness are very promising alternative to Nafion membrane in DMFC for their high chemical stability, thermal stability, high conductivity and better methanol resistance. However, proton conductivity of SPEEK membrane is lower than that of Nafion membrane. The demand of high proton conductivity calls for the SPEEK membranes to have a high degree of sulfonation(DS). Such membranes, however tend to swell excessively and lose their performance in the film. In order to solve the contradictions, we need to modified the SPEEK membranes.This work presented here synthesized three types of layered double hydroxide(LDH), they shared the same structure but different interlayer anion. First this work synthesized CO3-LDH, direct-SO4-LDH and indirect-SO4-LDH by coprecipitation method and other method. These LDH were characterizad and analyzed by X-ray diffraction(XRD), Scanning Electron Microscope(SEM), Energy Dispersive Spectrometer(EDS), Fourier transform infrared spectra(FT-IR), Thermal Gravimetric Analysis(TGA)coupled with Differential Scanning Calorimetry(DSC),etc. Two kinds of SPEEK which have different sulfonated degree were synthesized at the same time, and characterized by FTIR.Furthermore, recast method was used to prepare three types LDH/SPEEK composite membranes with the loading 2.5wt%, 5wt%, 7.5wt% and 10 wt % respectively. Various experimental techniques namely: SEM, TGA coupled with DSC, Ion Exchange Capacity(IEC), water uptake, methanol swelling, methanol permeability, proton conductivity and selectivity were employed to characterize the LDH/SPEEK composite membranes.The results showed that the higher interlayer distance of LDH, the higher water uptake, ions exchange capacity and proton conductivity of LDH/SPEEK composite membranes. When the doping amount is 7.5%, the vaule of water uptake, IEC and proton conductivity were the highest. The high sulfonated degree of SPEEK, the composite membranes have the higher proton conductivity, but also with the higher methanol swelling degree and methanol permeability. Results showed that when dop 7.5% direct-SO4-LDH into SPEEK(DS=65.2%), the composite membrane has the highest proton conductivity, 81.1 m S cm-1, which can compareble with Nafion115®. The selectivity of the composite membrane was two times higher than that of the blank SPEEK membrane, and higher than Nafion115®.