磺化聚酰亚胺膜在全钒液流电池中的应用及稳定性研究

发布时间：2018-01-10 20:37

本文关键词：磺化聚酰亚胺膜在全钒液流电池中的应用及稳定性研究　出处：《西南科技大学》2017年硕士论文　论文类型：学位论文

【摘要】：全钒氧化还原液流电池(VRFB)是一种新型绿色二次电池,具有容量可调、可深度充放电、效率高、操作维护简单、使用寿命长、成本低廉等优点。隔膜是VRFB的三大组件之一,起分隔正负极电解液以防止电池自放电、让质子透过以导通整个回路的作用。理想的VRFB隔膜应该具有质子传导率及化学/电化学稳定性高、钒渗透及价格低等特点。目前广泛使用的VRFB隔膜是全氟磺酸膜如美国杜邦公司生产的Nafion系列膜,其质子电导率及化学/电化学稳定性均较高,但钒渗透及价格均过高。因此,必须研发新型隔膜,使之满足在VRFB大规模产业化推广应用中的迫切需求。在众多的面向VRFB应用的新型隔膜研发中,合成并制备非氟高分子膜是一个重要的研究方向。与Nafion膜相比,非氟高分子膜通常具有钒渗透低、价格低的优势。然而,非氟高分子膜的稳定性问题是制约其在VRFB中长期使用的瓶颈。因此,迫切需要进行非氟高分子膜在VRFB中的降解机理研究,以阐明导致此类膜稳定性下降的根本原因。本文以磺化聚酰亚胺(SPI)膜为非氟高分子膜代表,通过原位和离线测试方法研究其在VRFB中的降解机理。对SPI膜及其低聚物在降解前后的形貌、结构、机械性能、理化特性等进行表征。光学照片和SEM图像结果显示,经过原位降解的SPI膜比经过离线降解显示出更严重的表面形貌破坏。经不同浸泡液浸泡后,SPI膜的机械性能和黏均分子量均不同程度地下降,且H+和V(V)均起到加速降解的作用。FTIR结果表明SPI膜上的磺酸基团在VRFB应用中未被降解,1H-NMR谱证实降解后的SPI膜发生了聚合物分子链断裂和酰亚胺环水解。XPS谱显示SPI的水解产物 NH2基团被氧化。基于所有实验研究结果,提出了SPI膜在VRFB中可能的两步降解机理,即水解和氧化步骤。为增加SPI膜的稳定性,制备了一系列磺化度从30%变化至70%的磺化聚酰亚胺/壳聚糖(SPI/CS)复合膜,并研究了它们的的VRFB性能。膜的结构和形貌通过ATR-FTIR和AFM表征,膜的理化性质被分别测试。研究结果显示,SPI30/CS膜具有最低的质子传导率和低到可忽略的钒渗透率。使用SPI30/CS膜的VRFB在10 m A cm~(-2)电流密度下性能较稳定,而在20、30 m A cm~(-2)及更高电流密度下均不能正常充放电,因SPI30/CS膜的质子传导率太低。尽管SPI70/CS膜的质子传导率最高(4.88×10~(-2) S cm-1),但是,使用SPI70/CS膜的VRFB在20~80 m A cm~(-2)电流密度下却具有最低的库伦效率,因为膜的钒渗透率亦最高(10.47×10-7 cm2min-1)。将SPI40/CS膜在50 m A cm~(-2)电流密度下进行了100个充放电循环,显示出较稳定的库伦效率(99.3%)和能量效率(70.5%)。综合考虑它们较高的质子选择性、较好的化学稳定性以及优异的VRFB性能,SPI40/CS及SPI50/CS膜均为面向VRFB应用的潜在选择。
[Abstract]:Total vanadium redox liquid flow battery (VRFB) is a new green secondary battery with adjustable capacity, deep charge and discharge, high efficiency, simple operation and maintenance, long service life. The diaphragm is one of the three major components of VRFB, separating the positive and negative electrolyte to prevent the self-discharge of the battery. The ideal VRFB diaphragm should have high proton conductivity and chemical / electrochemical stability. Vanadium permeation and low price. At present, the widely used VRFB membrane is perfluorinated sulfonic acid membrane, such as the Nafion series membrane produced by DuPont Company of the United States, its proton conductivity and chemical / electrochemical stability are relatively high. However, vanadium permeation and price are too high. Therefore, it is necessary to develop new diaphragm to meet the urgent need in the large-scale industrial application of VRFB. In many new diaphragm research and development for VRFB applications. Synthesis and preparation of non-fluorinated polymer membranes is an important research direction. Compared with Nafion membranes, non-fluorinated polymer membranes usually have the advantages of low vanadium permeation and low price. The stability of non-fluorinated polymer membrane is the bottleneck of its long-term use in VRFB. Therefore, it is urgent to study the degradation mechanism of non-fluorinated polymer membrane in VRFB. In order to elucidate the fundamental cause of the decrease of the stability of this kind of membrane, the sulfonated polyimide (SPI) membrane is represented by the non-fluorinated polymer membrane in this paper. The degradation mechanism of SPI film in VRFB was studied by in-situ and off-line measurements. The morphology, structure and mechanical properties of SPI film and its oligomer before and after degradation were studied. The results of optical photos and SEM images showed that the SPI films degraded in situ showed more serious surface morphology damage than those after offline degradation and were soaked in different soaking solutions. The mechanical properties and viscosity average molecular weight of SPI films decreased in varying degrees. The results of FTIR showed that the sulfonic groups on SPI films were not degraded in the application of VRFB. The 1H-NMR spectra confirmed that the degradation of SPI film resulted in the polymer molecular chain break and the hydrolysis of imide ring. XPS spectra showed that the hydrolyzed product of SPI was produced. The NH2 group is oxidized based on all experimental results. The possible two-step degradation mechanism of SPI membrane in VRFB, i.e. hydrolysis and oxidation steps, was proposed to increase the stability of SPI film. A series of sulfonated polyimide / chitosan / spi / CS composite membranes with sulfonation degree ranging from 30% to 70% were prepared. The structure and morphology of the films were characterized by ATR-FTIR and AFM, and the physicochemical properties of the films were tested. The SPI30/CS membrane has the lowest proton conductivity and negligible vanadium permeability. The VRFB using SPI30/CS membrane is 10 Ma / cm ~ (-2). The performance is stable at current density. But the charge and discharge can not be normal at 20 ~ 30 Ma / cm ~ (-2) and higher current density. Because the proton conductivity of SPI30/CS membrane is too low, although the highest proton conductivity of SPI70/CS membrane is 4.88 脳 10 ~ (-2) S cm ~ (-1), however. The VRFB using SPI70/CS film has the lowest Coulomb efficiency at the current density of 20 ~ 80 Ma / cm ~ (-2). Because the vanadium permeability of the membrane is also 10. 47 脳 10 ~ (-7) cm ~ (-2) min ~ (-1). The SPI40/CS membrane is 50 Ma / cm ~ (-2). 100 charge-discharge cycles were carried out at current density. It shows stable Coulomb efficiency (99.3) and energy efficiency (70.5%). Their higher proton selectivity, better chemical stability and excellent VRFB properties are considered. Both SPI40/CS and SPI50/CS films are potential options for VRFB applications.
【学位授予单位】：西南科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM912

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