Investigation Of Quercetin-based Proton Exchange Membrane With Prolonged Lifetime

Chemical degradation of proton exchange membrane(PEM)is one of the factors that limit the lifetime of proton exchange membrane fuel cell(PEMFC),it is of great significance to develop PEMs with prolonged lifetime.Free radical scavengers(FRS)are a series of compounds with the ability to scavenge reactive radical species,these compounds can mitigate chemical degradation of PEM,thus the lifespan of PEMFC could be enhanced.Quercetin,a natural antioxidant,is extracted from flowers,leaves and fruits of certain plants.Quercetin is the most potent antioxidant among flavonoids.In this thesis,quercetin was introduced to PEMs as FRS,researches have carried out as follow:(1)The oxidation-reduction potential of quercetin under acidic conditions was determined by cyclic voltammetry,and the antioxidative property of quercetin was evaluated through chromogenic experiment.The cyclic voltammetry curve indicates that quercetin has a pair of peaks at 0.084 V and 0.050 V,which proves that quercetin could transfer between oxidation state and reduced state under certain conditions.Chromogenic experiment showed that quercetin had certain antioxidant capacity under acidic conditions and could effectively reduce the degradation of rhodamine B in the system.(2)Nafion/quercetin composite membrane was fabricated through casting method successfully.Scanning electron microscopy(SEM)showed that the composite membranes prepared were pyknotic and the thickness was close to Nafion 211 membranes(25.4 ?m).Fourier transform infrared spectroscopy(FTIR)and thermogravimetric analysis(TGA)showed no chemical interaction between quercetin and functional groups of Nafion matrix,while the additional absorption peak at 1641.2 cm-1 in FTIR spectrum indicated the successful introduction of quercetin.Ion exchange capacity(IEC)test showed that the introduction of quercetin would reduce IEC of the composite membrane to a certain extent.If the content of quercetin was controlled in a low range,the high IEC loss could be effectively avoided.(3)The Nafion/quercetin composite membrane was assembled into a single cell,and the single cell test and accelerated degradation test(ADT)were performed.The polarization curves of single cell showed that the higher the quercetin content was,the worse the cell performance was.The performance loss could be controlled within a lower range if quercetin content is limited to 1%.The ADT showed that the voltage attenuation of the single battery assembled by Nafion/1%quercetin composite membrane was only 51 mV at 1000 mA/cm2 after 5 ADT cycles,which was far better than Nafion and Nafion/1%CeO2 composite membrane under the same test conditions.Moreover,after 9 ADT cycles,this index still had no significant attenuation.After nine ADT cycles,the hydrogen crossover current of Nafion/1%quercetin composite membrane was only 20.03 mA/cm2,while Nafion reached 21.33 mA/cm2 after the first ADT cycle.The same conclusion can be obtained from the OCV curve.SEM cross section image before and after ADT showed that the thickness reduction of Nafion/1%quercetin composite membrane was much small than that of Nafion,which proved that the presence of quercetin could effectively slow down the degradation of the composite membrane.FTIR test showed that quercetin could regenerate in PEM,which ensured that quercetin could play a long-term role in the membrane.