Electrical conductivity fiber electrode

Carbon fiber electrode - Edison produced the first carbon fibers by carbonization of cotton threads in 1879. Today polyacrylonitrile (as well as Rayon and various other organic precursors) is the most common precursor for carbon fiber formation [i]. Carbonization of polyacrylonitrile is carried out at 1500 °C to give highly electrically conducting fibers with 5-10 pm diameter. Fibers carbonized at up to 2500 °C are more graphitic with a carbon content of >99%. Carbon fiber-based materials have found many applications due to their exceptionally high tensile strength. In electrochemistry carbon fiber -> micro electrodes are very important in analytical detection [ii] and for in vivo electrochemical studies [iii]. Carbon fiber textiles are employed in - carbon felt electrodes. 

Fiber electrodes -> microelectrodes in a form of bare fibers as the conductive elements, protruding from the end of an insulator, usually made of carbon fibers of 7-8 pm diameter and sealed in glass capillaries often used for direct measurements (e.g., using fast cyclic voltammetry) of the in-vivo release of oxidiz-able neurotransmitters, such as dopamine, serotonin, norepinephrine, or epinephrine, from living cells. Also used to monitor electric activity of single nerve cells or for diagnostic purposes in electroanalysis. S ee also carbon fiber electrode. 

Electrosorption technique, which may use the electrical potential as the 3" driving force to the traditional adsorption and ion exchange mechanism, has reversible characteristics of purifying waste solution by adsorption and concentrating contaminants by desorption. Carbon materials satisfy the basic requirements for an efficient electrode material, and have good radiation and chemical-stability. Especially activated carbon fiber (ACF), which can be easily made into a variety of types (textures or sheet), has a high specific surfece area and electrical conductivity. 

Carbon fibers formed into filaments provide very compatible biomaterials. Carbon does not corrode in the body, nor does it generate a foreign body respon.se. Further, its high electrical conductivity suggests that a variety of electrode and conductor applications are possible. For example, filamentary carbon cathodes have been used to stimulate the growth of bone and soft tissues [136], when adjusting the level of current can be used to influence the growth. 

In this context, nanoporous carbons are extremely interesting materials which can be used either as electrodes of supercapacitors or hydrogen reservoir. They are commercially available at a low cost and under various forms (powder, fibers, foams, fabrics, composites) [3]. They can be obtained with well-developed and controlled porosity [4,5] and with a rich surface functionality [6,7], As far as electrochemistry applications are concerned, very important advantages of carbons are a high electrical conductivity, a good chemical stability in various electrolytic media and the possibility to control wettability by the nature of the surface functionality. When they are not playing the role of active material for the storage process, carbons may be also useful as additive in a composite to improve its physical properties. Particularly carbon nanotubes are able to improve the electrical conductivity and mechanical properties of electrodes [8],... 

Poly(vinyl pyrrolidone) (PVP) was used by Nguyen et al. as a polymer matrix to prepare electrically conducting nano(micro)poly(3,4-ethylenedioxythiophene) (PEDOT) fiber non-woven web [50]. The electrical conductivity of the electrospun PEDOT non woven web was as high as 7.5 S cm when 1-propanol was used as the solvent. An electrochemical capacitor was assembled using one pair of the PEDOT nonwoven webs as the electrodes by a simple stack method, where metal plates were used as current collectors. They observed the electrochemical charge and discharge behavior of the capacitor, confirming that the PEDOT nonwoven web can be used as an electrode for flexible electrochemical capacitors. 

Both carbon fiber/lead and alumina/lead composites have been utilized for the fabrication of electrodes in lead add batteries with a significant weight reduction. For example, reinforcing lead unidirectionally with 25 vol.% of a-alumina fibers increases the matrix stiffness by a factor of 20 and reduces the electrical conductivity only slightly. Due to the stiffening effect of the fibers, pure lead can be used instead of a complex alloy, thus reducing the cost of the matrix and improving its corrosion resistance [49]. 

However, to be able to introduce further functionality, additional synthesis steps on the structured electrodes could be performed. Branching of primary CNTs grown on graphite foil with secondary nanotubes has been demonstrated by Li et al. and Xia et al. [153, 154], resulting in the so-called hierarchically structured electrodes with high electrical conductivity. In a follow-up study, this concept has been transferred to hierarchically structured electrodes grown on carbon cloth, which is frequently used as GDL in fuel cell electrodes. After Pt deposition onto the carbon cloth/carbon fiber/CNT composites, reasonable activity for ORR was obtained [155]. The application of similar structures in fuel cells has also been reported and makes this approach a promising concept for the immediate future [156,157]. 

---