COMPARISON ELECTRICAL AND HYDRAULIC PROPERTIES OF CARBON FELT IN DIVERSE DIELECTRIC LIQUIDS

Carbon felt substance having permeable structure and significant surface for electrochemical redox reactions in electrolytes is a wide-spread material for electrodes in numerous applications such as redox flow batteries, fuel cells, electro-dialysis facilities, etc. Felt internal structure is composed by bonded together different lengths carbon filaments that resemble stochastically oriented channels having significantly changing cross-section and separated by carbon fibers. Felt hydraulic permeability is similar to a permeability of a porous media and is determined by internal empty volume and arrangement of carbon fibers. Its electro-conductivity is ensured by the closeness of carbon filaments yet mostly by the density of electrical interconnections between fibers. Both these properties (permeability and electrical conductivity) are extremely important for the efficient activities of electrochemical appliances. However, they are contradicting one to another when a felt is being pressed against the surface.

Compressed felt in spite of enhanced electrical and electrochemical parameters possess reduced hydrodynamic permeability as a result of a diminished volume of porous media and intrinsic channels. This circumstance causes increasing hydrodynamic expenditures of electrolyte pumping through electrodes and weakened cell (battery) efficiency. Designer of specific electrochemical system has to take into account both of these properties selecting optimal design of a cell.

Presented article provides the results of measurements of electrical and hydraulic properties of a carbon felt like a dry and immersed in several non-conductive liquids having different electrical permittivity. Obtained results were analytically analyzed and relations between liquid permittivity and electrical conductivity were found.