Activated carbon based electrodes

Zhou HT, Zhang HM, Zhao P, Yi BL. A comparative study of carbon felt and activated carbon based electrodes for sodium polysutfide/bromine redox flow battery. Electrochim Acta 2006 51 6304-12. 

Carbonaceous materials are almost exclusively utilized as active materials of double-layer electrodes due to their high conductivity, electrochemical stability, and porosity. Activated carbons still constitute the most practical active carbon-based electrode materials. They have high surface areas, are inexpensive to produce, and can be fabricated using a variety of readily available precursor materials. 

The general aim of this work is to show the properties of activated carbon-ionic liquid interface (AC-IL) as well as performance of capacitors based on activated carbons as electrode materials and ionic liquids as electrolytes. 

As in the case with PAFC s, voltage obtained from an AFC is affected by ohmic, activation, and concentration losses. Figure 4-7 presents data obtained in the 1960 s (18) which summarizes these effects, excluding ohmic losses, for a catalyzed reaction (0.5-2.0 mg noble metal/cm ) with carbon-based porous electrodes for H2 oxidation and O2 reduction in 9 N KOH at 55-60 C. The electrode technology was similar to that employed in the fabrication of PAFC electrodes. Performance of AFC s with carbon-based electrodes has not changed dramatically since these early results were obtained. 

Some indolylthiohydantoin derivatives that have aldose reductase inhibitory activity [75] were investigated electroanalytically by voltammetric determination. Based on this study, a simple, rapid, sensitive and validated voltammetric method was developed for the determination of the compounds that are readily oxidized at carbon-based electrodes. Oxidation of the indolic compounds occurs on the nitrogen atom in the indole ring of the molecule [162]. 

Other types of carbon-based electrodes, such as activated carbon (Canizares et al. 1999), graphite particles (Piya-areetham et al. 2006), graphite Rashig rings (Ogutveren et al. 1999), and carbon black slurry (Boudenne et al. 1996 Boudenne and Cerclier 1999) have also been employed sometimes for the treatment of organic compounds. 

An approach focused on fabrication of nanostructured three-dimensional electrodes and introduction of surface modifications for tethering/retention in an optimal orientation of the MCOs to permit DET to the Tl site from the electrode shows great promise for the production of biocathode prototypes for application to EFCs. A systematic study of such electrodes modified with each of the MCOs available, reporting on their activity for ORR, using DET, under defined conditions of pH, mass transport, and temperature is not yet available, and would be a valuable contribution to advance the technological application of EFCs. A welcome recent focus is normalization of ORR, based on DET to Trametes versico/or adsorbed on porous carbon-based electrode materials, to electrode volume and to electrode... 

Recent developments include the use of hybrid electrochemical capacitors, in which intercalations compounds (Li/ri Oij) were used as the negative material and activated carbon was used as the positive material (Amatucci et al., 2001). Cheng et al. (2006) have recently reported a P-FeOOH-based hybrid capacitor where the iron hydroxide, acting as negative electrode, is assembled with activated carbon positive electrode in ethylene carbonatc/di methyl carbonate with 1.0 M LiPFg electrolyte. 

Fan, Z. et al.. Asymmetric supercapacitors based on graphene/MnOj and activated carbon nanofiber electrodes with high power and energy density. Adv. Funct. Mater. 2011,27(72 , 2366-2375. 

Cericola, D., R. Kbtz, and A. Wokaun. 2011. Effect of electrode mass ratio on aging of activated carbon based snpercapacitors utilizing organic electrolytes. Journal of Power Sources 196 3114-3118. 

It is worthwhile to note that the ORR activity on carbon-based electrode surface is strongly dependent on the pretreatment such as polishing, dipping a carbon electrode into chromic acid, exposing to radio frequency plasma in oxygen atmosphere, and... 

Industrial supercapacitors are essentially based on nanoporous carbon electrodes. The reasons of the choice lie in the high availability, low cost, chemical inertness, and good electrical conductivity of activated carbons, as well as a high versatility of texture and surface functionality. For these reasons, this chapter will present the capacitance properties of carbon-based electrodes showing optimization strategies playing on the structure/nanotexture of carbon and the nature of the electrolyte. 

Another option for carbon-based electrodes is to coat poorly conductive CP electrodes with highly conductive activated carbon powders to increase the amount of electrochemically active surface area available for redox reactions to occur. An example of such an activated carbon powder was photographed under an optical microscope and presented in Fig. 3.3. Unscreened powder (i.e. with particles of... 

However, carbon-based electrodes often show inadequate electrochemical activity and kinetic reversibility toward the electrochemical reactions [34]. Various approaches, including heat treatment, chemical treatment, electrochemical oxidation, and doping (or depositing) with metals on carbon fibers, have been applied to improve electrochemical activity. 

The layer capacitance is strongly influenced by the pore structure of the electrode therefore, the pore structure and surface chemistry of the activated carbons are very important. Many papers and reviews on these subjects have been published [6-8]. The high capacitance (100 200 Fg for single electrode in organic electrolyte) is due to the high specific surface area (>1,000 m g ) provided by the many micropores. In general, it is believed that there is a proportional correlation between the specific surface area and the electric double-layer capacitance of the activated carbons based on the following equation. 

For the oxygen reduction catalysts used in carbon-based electrode, it is very important that these show the direct 4-electron reduction which does not produce peroxide or these have very high catalytic activity to decompose peroxide which is produced on carbon. 

Organophosphorus compounds are significant major environmental pollutants due to their intensive use as pesticides. The modem techniques based on inhibition of cholinesterase enzyme activity are discussed. Potentiometric electrodes based on detection of cholinesterase inhibition by analytes have been developed. The detection of cholinesterase activity is based on the novel pindple of molecular transduction. Immobilized peroxidase acting as the molecular transducer, catalyzes the electroreduction of hydrogen peroxide by direct (mediatorless) electron transfer. The sensing element consists of a carbon based electrode containing an assembly of co-immobilized enzymes cholinesterase, choline oxidase and peroxidase. 

Further investigations are required to develop active carbon-based materials with higher capacitances and electrode arrangements favorable to mass transport. Moreover, inexpensive, upscalable fabrication techniques for these materials are also required to render them commercially viable. 

The conductivity of the electrode is cmcial factor for fast-response actuators. Unfortunately without improvements in the electrode conductivity, the porous carbons are not able to work at excitation frequencies higher than 1 Hz (Palmre et al. 2012 Sugino et al. 2009). One way is to tune the properties of carbon by choosing suitable precursors and synthesis conditions however, as discussed above, another approach to enhance the electrical conductivity of carbon-based electrodes is to combine amorphous carbon with carbon having higher electrical conductivity, such as CNTs with CDC, CNTs, or vapor-grown carbon nanofibers with activated carbon nanofibers or with carbon black. 

This system typically uses sulfuric acid as the electrolyte with a proton exchange membrane. While a porous separator could be used, for high efficiency operation, ion-selective membranes are generally preferred as vanadium crossover leads to losses in coulombic efficiency. At present, Nafion is the membrane of choice as V(V) is a powerful oxidizing agent, which can attack cheaper hydrocarbon-based ion selective membranes [21]. The redox reactions of different vanadium species have displayed reversibility and high activity on carbon based electrodes. Moreover, Li et al. discovered the catalytic effects of bismuth nanoparticles on V(II)/V(III) [51] and of niobium oxide nanorods on both V(II)Af(lII) and V(IV)Af(V) [52], which have been shown to further enhance the energy efficiency of the VRB by more than 10 %. 

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