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Abstract
Electro-conductive carbon felt (CF) material is composed by bonding together different lengths of carbon filaments resulting in a porous structure with a significant internal surface that facilitates enhanced electrochemical reactions. Owing to its excellent electrical properties, CF is found in numerous electrochemical applications, such as electrodes in redox flow batteries, fuel cells, and electrochemical desalination apparatus. CF electro-conductivity mostly arises from the close contact between the surface of two electrodes and the long carbon fibers located between them. Electrical conductivity can be improved by a moderate pressing of the CF between conducting electrodes. There exist large amounts of experimental data regarding CF electro-conductivity. However, there is a lack of analytical theoretical models explaining the CF electrical characteristics and the effects of compression. Moreover, CF electrodes in electrochemical cells are immersed in different electrolytes that affect the interconnections of fibers and their contacts with electrodes, which in turn influence conductivity. In this paper, we investigated both the role of CF compression, as well as the impact of electrolyte characteristics on electro-conductivity. The article presents results of measurements, mathematical analysis of CF electrical properties, and a theoretical analytical explanation of the CF electrical conductivity which was done by a stochastic description of carbon filaments disposition inside a CF frame.
Highlights
Carbon Felt (CF) is used as electrode material in a variety of electrochemical applications [1,2,3,4,5,6,7].Currently, its most prominent utilization is in the vanadium redox and other flow type batteries owing to its good electrical conductivity, hydraulic permeability, and durability in strong acid and alkali electrolytes
Its most prominent utilization is in the vanadium redox and other flow type batteries owing to its good electrical conductivity, hydraulic permeability, and durability in strong acid and alkali electrolytes
Good electrical conductivity arises from the movement of electrons through the carbon filaments to reach the electrolyte [8,9,10,11,12,13,14,15,16,17,18,19,20]
Summary
Carbon Felt (CF) is used as electrode material in a variety of electrochemical applications [1,2,3,4,5,6,7]. Work by Johan et al [26] was the first to examine conductivity of CFs used in electrochemical applications These authors studied a new bipolar cell with a proton-exchange membrane, where flat electrodes were made of long carbon fiber assemblies like CF structure to facilitate electrical current flow. The same sharp diminishing of resistance versus compression pressure was detected, which may be described by an exponential formula, with different exponent coefficients These coefficients depend on the type of adhesive used; the significant achievement of Johan et al.’s work [26] is that for the first time their values were represented as a function of the kind of adhesive and the type of electrodes design. The experimental measurements were compared with the results of the developed theoretical model
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