【作者】 李萍；

【导师】 刘金盾； 王景涛；

【作者基本信息】 郑州大学 ， 化学工艺， 2019， 硕士

【摘要】 质子交换膜燃料电池（Proton exchange membrane fuel cell,PEMFC）作为新型清洁能源技术的代表,可将燃料的化学能直接、高效地转化为电能。质子交换膜（PEM）是PEMFC的核心组件,质子需穿过PEM从阳极到达阴极以完成能量转化。静电纺丝技术制备的纤维具有高比表面积、高孔隙率、纳米级直径,被认为是一种良好的质子导体。同时,为满足低燃料渗透率,可在纤维间的微孔中填充高分子基质制备纳米纤维复合膜（Nanofibrous composite membrane,NFCM）。但由于纤维沿水平向取向,造成膜水平向传导率远高于垂直向传导率,质子传导存在严重的各向异性。而实际应用中垂直向质子传导率决定着燃料电池的性能。因此强化NFCM垂直向质子传递性能是实现高性能NFCM制备及其应用推广的关键。本论文围绕在膜垂直向构建高效质子传递通道和优化质子传递位点两个方面开展工作。首先通过制备多孔纤维,在纤维表面和内部造孔,并诱导质子传导基团沿孔壁富集,在膜垂直向形成低阻力传递通道;此外,将传导性的无机纳米填充物与聚合物混合纺丝,制备杂化纤维,增加纤维内部传递位点数量,连通垂直向传递死区,并考察多孔结构、孔壁基团排布、无机质子导体亲疏水性以及界面处酸碱对协同作用对垂直向质子传递性能和质子传递各向异性的影响。具体研究内容和主要结论概述如下:（1）多孔NFCM的制备及传递特性研究。首先采用离子液体（Ionic liquid,IL）软模板法制备多孔Nafion纤维,随后采用流延法在纤维间孔隙中填充碱性高分子基质壳聚糖（Chitosan,CS）后制备多孔NFCM。利用沿着孔壁形成的界面通道,沿着孔壁富集的-SO₃H以及Nafion纤维上的-SO₃H基团与CS上的–NH/–NH2在两相界面处形成的酸碱对,在膜垂直向形成高效质子传递通道,强化膜有水/无水条件下的垂直向质子传导率。结果表明:在90℃和100%RH以及120℃和0%RH条件下,相比于NFCM,多孔NFCM的垂直向质子传导率分别提高了3.2倍和2.7倍,同时,质子传递各向异性显著降低。（2）杂化NFCM的制备及传递特性研究。首先制备了两种尺寸为2-5 nm的量子点（QDs）:亲水性的聚合物量子点（PQD）和疏水的氧化石墨烯量子点（GQD）。PQD上含有大量的–CO₂H和–NH–/–NH₂基团,而GQD上大部分官能团被碳化。随后将其分别与磺化聚醚醚酮（Sulfonated polyether ether ketone,SPEEK）混合纺丝,制备SPEEK/QDs杂化纤维,最后浇铸CS溶液制备杂化NFCM。研究发现,PQD与SPEEK链段上的-SO₃H基团产生强的相互作用,实现了无机质子导体PQD在纤维中的均匀分散且高填充,且在纤维与无机导体界面区域形成额外的传递通道。此外,PQD上的-NH-/-NH₂基团与SPEEK上的-SO₃H基团形成酸碱对,形成低阻质子传递位点,连通了纤维垂直向传递“死区”。结果显示,100%RH、90℃条件下,CS/SP/PQD-30%的垂直向传导率达到399 mS cm^-1,较空白膜提升了224%。在120℃无水条件下,CS/SP/PQD-30%的垂直向和水平向传导率分别为451和525 mS cm^-1,分别是空白膜的3.2和1.8倍,且质子传递各向异性从空白膜的2.11降低到1.16。更多还原

【Abstract】 Proton exchange membrane fuel cell（PEMFC）,as a representative of new clean energy technologies,can directly and efficiently convert the chemical energy of fuel into electrical energy.Proton exchange membrane（PEM）is the core component of PEMFC,protons need to pass through the PEM from the anode to the cathode to complete the energy conversion.The nanofiber prepared by the electrospinning technology has the characteristics of large specific surface area,high porosity,and nanoscale diameter and is considered to be a good proton conductor.Meanwhile,in order to meet the requirement of low fuel permeability,dense nanofiber composite membrane（NFCM）can be prepared by filling the gaps among nanofibers with polymer matrix.However,these NFCMs confront serious proton transfer anisotropy,i.e.,the through-plane conductivity is generally much lower than that of in-plane conductivity,due to the preferential horizon-direction alignment of nanofibers.While,it is the through-plane proton conductivity that,determines the fuel cell performance in practical application.Therefore,intensifying the through-plane proton conductivity is the key to the preparation and application of high-performance NFCM.This paper focused on the construction of efficient proton transfer channels and optimization of proton transfer sites in the vertical direction of the membrane.First,through the preparation of porous nanofibers,nanopores were formed on the surface and inside of the nanofibers and the proton-conducting groups inside nanofiber were induced to enrich along pore walls.And thus formed low-energy-barrier transfer channel in the vertical direction of the membrane;In addition,conductive inorganic nanofillers were uniformly dispersed in the nanofiber to prepare hybrid nanofiber.In such way,the number of transfer sites inside the nanofiber were increased and the vertical direction“transfer dead zone”was connected.The effect of the porous structure,the arrangement of pore wall groups,the hydrophilic and hydrophobic properties of the inorganic proton conductor,and the synergistic effects of acid-base pairs at the interface on the vertical proton transfer performance and proton transfer anisotropy was investigated.The specific research contents and main conclusions are summarized as follows:（1）The preparation of porous NFCM and study on proton conduction intensification.Firstly,porous Nafion nanofiber was fabricated through ionic liquid（IL）soft template methods.The resultant porous nanofiber mat was then impregnated with basic chitosan（CS）matrix to prepare porous NFCM.The abundant pores inside porous nanofiber provided numerous vertical transfer channels at interfaces between CS and pore walls.Meanwhile,the–NH/NH₂ groups on CS formed acid-base pairs with-SO₃H group on Nafion along pore walls.These stable vertical pathways significantly facilitated the through-plane proton conduction at both hydrated and anhydrous conditions.The results indicated that the through-plane proton conductivity of porous NFCM were increased by 3.2 and 2.7 times of that of NFCM at 90 ^oC and 100%RH,and 120 ^oC and 0%RH,respectively,and the proton transfer anisotropy was significantly decreased.（2）The preparation of hybrid NFCM and study on proton conduction intensification.First,two types of quantum dots（QDs）with a size of 2-5 nm were prepared:hydrophilic polymer quantum dots（PQD）and hydrophobic graphene oxide quantum dots（GQD）.PQD contained a large number of–CO₂H and–NH–/–NH₂groups,and most of the functional groups on GQD were carbonized and had strong hydrophobicity.Then,the SPEEK/QDs hybrid nanofiber was prepared by blending QDs and sulfonated polyether ether ketone（SPEEK）.The resultant hybrid nanofiber mat was then impregnated with CS matrix to prepare hybrid NFCM.It was found that PQD and the-SO₃H group on the SPEEK had strong interaction,and thus achieved PQD uniform dispersion and high loadings in the nanofiber.And then additional transfer channel were constructed at interfaces between nanofiber and inorganic conductor.Additionally,the–NH-/-NH₂ group on PQD formed acid-base pairs with-SO₃H group on SPEEK and thus formed low-energy-barrier proton transfer site.And the vertical direction“transfer dead zone”of nanofiber was connected.The results showed that CS/SP/PQD-30%achieved a through-plane proton conductivity of 399mS cm^-1 at 100%RH and 90 ^oC,which was 224%higher than that of plain membrane under indentical conditions.Under anhydrous conditions（120 ^oC）,the through-plane and in-plane conductivity of CS/SP/PQD-30%were 451 and 525 mS cm^-1,respectively,which was 3.2 and 1.8 times higher that of plain membrane,respectively.And the anisotropy decreased remarkdly,from 2.11 for the plain membrane to 1.16for CS/SP/PQD-30%.更多还原