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Electric and Hydraulic Properties of Carbon Felt Immersed in Different Dielectric Liquids

机译：浸在不同介电液体中的碳毡的电学和水力学性质

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Electroconductive carbon felt (CF) material, having a permeable structure and significant electroconductive surface, is widely used for electrodes in numerous electrochemical applications such as redox flow batteries, fuel cells, electrochemical desalination apparatus, etc. The internal structure of CF is composed of different lengths of carbon filaments bonded together. This structure creates a large number of stochastically oriented and stochastically linked channels that have different lengths and cross sections. Therefore, the CF hydraulic permeability is similar to that of porous media and is determined by the internal empty volume and arrangement of carbon fibers. Its electroconductivity is ensured by the conductivity of the carbon filaments and by the electrical interconnections between fibers. Both of these properties (permeability and electrical conductivity) are extremely important for the efficient functioning of electrochemical devices. However, their influences counter each other during CF compressing. Increasing the stress on a felt element provides supplementary electrical contacts of carbon filaments, which lead to improved electrical conductivity. Thus, the active surface of the felt electrode is increased, which also boosts redox chemical reactions. On the other hand, compressed felt possesses reduced hydrodynamic permeability as a result of a diminished free volume of porous media and intrinsic channels. This causes increasing hydrodynamic expenditures of electrolyte pumping through electrodes and lessened cell (battery) efficiency. The designer of specific electrochemical systems has to take into account both of these properties when selecting the optimal construction for a cell. This article presents the results of measurements and novel approximating expressions of electrical and hydraulic characteristics of a CF during its compression. Since electrical conductivity plays a determining role in providing electrochemical reactions, it was measured in dry conditions and when the CF was immersed in several non-conductive liquids. The choice of such liquids prevented side effects of electrolyte ionic conductivity impact on electrical resistivity of the CF. This gave an opportunity to determine the influences of dielectric parameters of electrolytes to increase or decrease the density of interconnectivity of carbon fibers either between themselves or between them and electrodes. The experiments showed the influence of liquid permittivity on the conductivity of CF, probably by changing the density of fiber interconnections inside the felt.
机译：具有渗透性结构和显着导电表面的导电碳毡（CF）材料被广泛用于许多电化学应用中的电极，例如氧化还原液流电池，燃料电池，电化学脱盐设备等。CF的内部结构由不同的组成长度的碳丝粘结在一起。这种结构产生了大量具有不同长度和横截面的随机定向和随机链接的通道。因此，CF的水力渗透率类似于多孔介质的渗透率，并由内部的空体积和碳纤维的排列方式决定。碳丝的导电性和纤维之间的电互连确保了它的导电性。这两个特性（磁导率和电导率）对于电化学装置的有效运行极为重要。但是，它们的影响在CF压缩期间会相互抵消。增加毛毡元件上的应力会提供碳丝的辅助电接触，从而改善电导率。因此，毡电极的活性表面增加，这也促进了氧化还原化学反应。另一方面，由于多孔介质和固有通道的自由体积减小，压缩毡的流体动力渗透性降低。这导致电解质通过电极泵送的流体动力消耗增加，并降低了电池（电池）效率。当选择电池的最佳结构时，特定电化学系统的设计者必须考虑这两个属性。本文介绍了CF压缩期间的测量结果以及电气和液压特性的新颖近似表达式。由于电导率在提供电化学反应中起着决定性的作用，因此应在干燥条件下以及将CF浸入几种非导电液体中时进行测量。这种液体的选择防止了电解质离子电导率影响CF的电阻率的副作用。这为确定电解质的介电参数的影响提供了机会，以增加或减少碳纤维在它们之间或在它们与电极之间的互连密度。实验表明，液体电容率对CF导电率的影响可能是通过改变毡内部纤维互连的密度来实现的。

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