【作者】 杨帆；

【导师】 何荣桓；

【作者基本信息】 东北大学 ， 化学， 2022， 硕士

【摘要】 随着人们对获取可持续能源的兴趣日益浓厚,钒氧化还原液流电池(VRFB)由于其成本低、寿命长、容量大、响应时间快等独特优势,被认为是一种具有广阔前景的储能设备。质子交换膜(PEM)作为VRFB的关键组成部分,在电极间离子的转移和抑制正、负极电解质的交叉混合方面起着至关重要的作用。VRFB的理想PEM应表现出高质子传导性以提供电池的高电压效率,以及低的钒渗透率以确保高库仑效率,并最终实现低水迁移以延长循环寿命。采用聚氯乙烯(PVC)和聚乙烯吡咯烷酮(PVP)的共混高分子聚合物作为膜材料制备PEM。并引入1-(3-氨基丙基)咪唑(APIm)作为功能官能团,直接与PVC进行亲核取代反应,构建质子传导网络。最后,以多孔聚四氟乙烯(?)(PTFE(?))增强膜作为骨架,进一步增强复合膜的机械强度和对钒离子的抗渗性。首先制备一系列不同比例的PVC-PVP混合膜,其中PVP起到传导质子的作用,而PVC起到骨架支撑作用,探究了 PVC和PVP的比例变化对膜的性能的影响。其中PVC含量增加,膜的机械性能增强;PVP含量增加,膜的电导率变高。为了进一步提高电池效率,将APIm添加到PVC-PVP溶液中以制备高酸掺杂水平的膜。首先固定PVC和PVP的质量比,然后改变PVC和APIm的摩尔比,制备出一系列不同比例的复合膜。实验发现,随着APIm含量的增加,PVC-PVP复合膜的吸水率和酸掺杂水平显著增加,膜的微相分离形态得到优化,并有效的降低了复合膜的面电阻。充放电测试结果表明,用PP-33%APIm膜的VRFB单体电池与Nafion117膜相比表现出更低的充电电压平台和更高的放电电压平台,然而,APIm中的咪唑基团可能会导致膜的高渗透性和机械性能下降,从而降低膜的循环稳定性。为了提高所制备膜样品的机械性能和长期循环稳定性,使用PTFE(?)增强的方法,将聚合物的混合溶液填充到PTFE(?)膜中,制备出具有三明治结构的PTFE增强膜。疏水性聚四氟乙烯基体的存在提高了膜的质子选择性、氧化稳定性和机械性能。实验发现,硫酸(SA)掺杂的PTFE/PP-50%APIm复合膜在室温下质子电导率为85 mS cm-1,拉伸强度可达45 MPa,而原始的PVP-PVC膜电导率仅为15 mS cm-1,拉伸强度为16MPa。在电流密度为20至120 mA cm-2时,PTFE/PP-33%APIm膜组装的VRFB的平均EE为84.8%,高于Nafion 117(76.7%)组装的电池的能量效率,获得了较好的电池性能。除此之外,PTFE/PP-33%APIm复合膜可稳定循环不低于50圈,并且其运行50圈容量保持率为56.9%。更多还原

【Abstract】 With the growing interest in sustainable energy,vanadium redox flow batteries(VRFB)are considered as a promising energy storage device due to their unique advantages such as low cost,long lifetime,large capacity,and fast response time.Proton exchange membranes(PEM),as the key component of VRFB,play a crucial role in ion transfer between electrodes and block the cross-mixing of positive and negative electrolytes.The desired PEMs for VRFBs should exhibit high proton conductivity for high voltage efficiency of the battery,as well as possess low vanadium permeability to ensure high Coulombic efficiency,and ultimately low water transport for long cyclinge life.The blended polymers of polyvinyl chloride(PVC)and polyvinylpyrrolidone(PVP)were employed as the basis materials to prepare the membranes of the PEMs by grafting functional groups of 1-(3-aminopropyl)imidazole(APIm)onto PVC via nucleophilic substitution reaction to construct a proton conducting network.Using the porous polytetrafluoroethylene(?)(PTFE)reinforced membrane as the skeleton to fabricate composite membranes by impregnating with the modified copolymers for enhanced mechanical strength and impermeability to vanadium ions.A series of PVC-PVP blend membranes with different ratios were first prepared.The PVC acts as the skeleton support and the PVP could transfer protons.The ratio of PVC and PVP was optimized and the properties of the membranes were investigated.The higher PVC content results in enhanced mechanical properties,and the higher conductivity arises from the high content of the PVP of the membranes.To further improve the cell efficiency,1-(3-aminopropyl)imidazole(APIm)was introduced to the PVC-PVP blended polymer high acid doping levels of the membranes.Fixing the mass ratio of PVC and PVP,a series of composite membranes were prepared by adjusting the molar ratio of PVC and APIm.The experimental results indicate that the high APIm content brings on high water uptake and acid doping level of the PVP-PVC blend membranes.A suitable microphase separation was formed in the membrane,and the area specific resistance of the composite membrane was effectively reduced.The charge and discharge test showed that the single battery with the PP-33%APIm membrane exhibited lower charge voltage platform and higher discharge voltage platform than that with the commercial Nafion117 membrane.However,the highly introduced imidazole groups in APIm may lead to the high permeability and decreased mechanical properties of the membranes,which would reduce the cycling stability of the membranes.In order to improve the mechanical properties and long-term cycling stability of the prepared membrane samples,the porious polytetrafluoroethylene(PTFE)membrane was employed to fabricate reinforced membranes.The mixed APIm modified PVC-PVP polymer solution was filled into PTFE holes to prepare PTFE reinforced membranes.The presence of hydrophobic PTFE improves the proton selectivity,oxidative stability and mechanical properties of the membranes.The experimental results indicate that the proton conductivity and the tensile stress at break of the sulfuric acid(SA)doped PTFE/PP-50%APIm composite membrane is 85 mS cm-1 and 45 MPa at RT,respectively.While the original PP membrane only exhibits a proton conductivity of 15 mS cm-1 and a tensile stress at break of 16 MPa.At current densities increased from 20 to 120 mA cm-2,the mean energy efficiency of the VRFB with the diaphragm of PTFE/PP-33%APIm is 84.8%,which is higher than that of the one with Nafion117(76.7%).In addition,the PTFE/PP-33%APIm composite membrane can be stably cycling at least 50 cycles,and its capacity retention rate is 56.9%after 50 cycles.更多还原