Composite-based electrodes

Fig. 37. Composite base electrode (left) and active materials (right) for batteries (a)-(d) for details, see the text.

Composite based electrodes have shown improved selectivity by inhibiting the interference reaction at the electrode. The large surface area, electrochemical properties, catalytic abilities and inherent biocompatibility make composites suitable for use in amperometric biosensors. Composites of gold nanopaiticles carbon based materials, Prussian blue nanopaiticles have been utilized for the fabrication of electrochemical... 

The use of corona-forming and precipitation electrodes made of a composite based on polypropylene and acetylene black (8 per cent by volume) is among the examples... 

Surface Composition and Depth Profiling of Ruthenium-Iridium Based Electrodes... 

Fig. 10. Ruthenium over titanium ratio for mixed (Ru, Ti)02 based electrodes prepared by thermal decomposition. Nominal compositions are given in the figure. After [46],...

Polymers have served roles in PEM fuel cell cathodes such as modifiers to macrocycle-based electrodes to improve conductivity and stability,165 composite materials with heteropolyacids,166 and as precursors to pyrolyzed catalysts.38,112,132,133 However, as discussed in the previous section, the activity of nitrogen-containing carbon raises the possibility of non-metal electrodes functioning in a cathode environment. Likewise, researchers have noted ORR activity for various conducting polymers containing nitrogen, and recently studies on their potential use in PEM fuel cell cathodes have been reported. 

Kamarajugadda, S., and Mazumder, S. Numerical investigation of the effect of cathode catalyst layer structure and composition on polymer electrolyte membrane fuel cell performance. Journal of Power Sources 2008 183 629-642. Krishnan, L., Morris, E. A., and Eisman, G. A. Pt black polymer electrolyte-based membrane-based electrode revisited. Journal of the Electrochemical Society 2008 155 B869-B876. 

A model of such structures has been proposed that captures transport phenomena of both substrates and redox cosubstrate species within a composite biocatalytic electrode.The model is based on macrohomo-geneous and thin-film theories for porous electrodes and accounts for Michaelis—Menton enzyme kinetics and one-dimensional diffusion of multiple species through a porous structure defined as a mesh of tubular fibers. In addition to the solid and aqueous phases, the model also allows for the presence of a gas phase (of uniformly contiguous morphology), as shown in Figure 11, allowing the treatment of high-rate gas-phase reactant transport into the electrode. 

More recently, Qu et al. examined composite Ru02/Ti02 nanotube and nanoparticle platinum electrodes [66], In a 0.5 M NaHC03 solution at -0.8V (versus SCE), the nanoparticle-based electrodes yielded faradaic efficiencies for methanol of 40%, compared to 61% for the nanotube composites However, no explanation was offered as to why the nanotube-based electrodes provided an increased catalytic activity. 

N. Pena, R. Tarrega, A.J. Reviejo and J.M. Pingarron, Reticulated vitreous carbon-based composite bienzyme electrodes for the determination of alcohols in beer samples, Anal. Lett., 35(12) (2002) 1931-1944. 

B. Serra, A.J. Reviejo, C. Parrado and J.M. Pingarron, Graphite-Teflon composite bienzyme electrodes for the determination of L-lactate application to food samples, Biosens. Bioelectron., 14(5) (1999) 505-513. A.A.J. Torriero, E. Salinas, F. Battaglini and J. Raba, Milk lactate determination with a rotating bioreactor based on an electron transfer mediated by osmium complexes incorporating a continuous-flow/ stopped-flow system, Anal. Chim. Acta, 498(1-2) (2003) 155-163. 

Bond, A.M., Czerwinski, W.A. and Llorente, M. (1998) Comparison of direct current, derivative direct current, pulse and square wave voltammetry at single disc, assembly and composite carbon electrodes stripping voltammetry at thin film mercury microelectrodes with field-based instrumentation. Analyst, 123, 1333-1337. 

The screen-printing paste is made up in the manner described in Section 4.2.2 and the patterns printed. The heater element and its leads would typically be platinum and the interdigitated electrodes gold. As illustrated below (Fig. 4.49) the heater might also be a composition based on ruthenium oxide (see Section 4.2.2). The contacting tabs are also screen-printed gold. 

Klapste, Bretislav Vondrak, Jiri Velicka, Jana. MnOx/C composites as electrode materials II. Reduction of oxygen on bifunctional catalysts based on manganese oxides. Electrochimica Acta (2002) 47(15) 2365-2369. 

Composite graphite electrodes based on metal hydrides (YH3, LaH3, CeH3 and GdH3) were for the first time used in the synthesis of EMFs containing soot. The use of metal hydrides instead of metal sward afforded electrodes with metals more homogeneously distributed in a graphite rod that provided more stable electric arc... 

For the first time the possibility of the use of metal (La, Y) hydrides to prepare composite graphite electrodes was studied. The yield of DCB extracts of C2n/M C82 (M = Y, La, Ce, Gd) from soot obtained by evaporation of composite electrodes based on YH3, LaH3, CeH3 or GdH3 is 2-3 % higher (4-5 wt. % of the primary soot) than the yield of the extracts from soot synthesized using the electrodes based on metallic yttrium, lanthanum, cerium or gadolinium. EMF.v Y2 C84 and Ce2 C78 were produced, separated, and isolated for the first time. Their purity was justified by S8-MALDI mass spectrometry and they were characterized by UV-Vis-NIR absorption spectroscopy. 

Ceria affords a number of important applications, such as catalysts in redox reactions (Kaspar et al., 1999, 2000 Trovarelli, 2002), electrode and electrolyte materials in fuel cells, optical films, polishing materials, and gas sensors. In order to improve the performance and/or stability of ceria materials, the doped materials, solid solutions and composites based on ceria are fabricated. For example, the ceria-zirconia solid solution is used in the three way catalyst, rare earth (such as Sm, Gd, or Y) doped ceria is used in solid state fuel cells, and ceria-noble metal or ceria-metal oxide composite catalysts are used for water-gas-shift (WGS) reaction and selective CO oxidation. 

Raney nickel electrocatalysts have also found useful applications as active electrodes for the HER (179, 180). The activity of Raney Ni catalysts is established after leaching out the base metal, Al or Zn. Choquette et al. (181) have examined the changes in morphology and composition of Raney-Ni composite catalytic electrodes accompanying dissolution of the base metal in concentrated NaOH. The depletion of Al from the Raney particles is, of course, accompanied by a major increase in real area with time of leaching and also, interestingly, with possible phase transformations (181). The electro-catalytic activity is, however, surprisingly, practically independent of time. 

Fig. 27. Cyclic curves for polypyrrole/c.b. composites, d = 300 pm, p = 71%, 7 = 0.5 mAJcnr Electrolyte 0.2 m LiC104 in PC. ITie base electrode is c.b.-filled PP.

The uncertainties regarding che actual topography of the layer obtained after emersion and subsequent transfer into the main UHV chamber precludes a precise determination of its thickness and composition based solely on the AES data. If one assumes, however, that the layer consists of a smooch nickel oxide and/or oxyhydroxide film interposed between the underlying metal and an equally smooch KOH overlayer che K/Ni signal is consistent with the presence of the equivalent of up to three molecular layers of KOH. This indicates chat the film of electrolyte that remains on the electrode surface after the electrolyte absorption step is on the order of a few nm. It must... 

Another problem arises in the case of weak or moderate adsorption [46]. When the sign of the potential drop across the diffuse layer changes with solution composition or electrode charge density, there is a change in the nature of the predominant ion at the oHp. Since different ions have different sizes, the position of the oHp also changes. Ionic size effects are not considered in the GC model of the diffuse layer. Thus, use of the model based on equation (10.8.10) must consider the possibility that and K d vary with adsorbed charge density Oad for constant charge density 0 on the electrode [46]. 

A. Yoshizawa, M. Takeda, Y. Oura, Y. Takemoto and K. Naoi, Low-molecular-weight soluble polyaniline for electrolytic capacitor, Electrochemistry, 1999, 67, 45 H. Yamamoto, K. Kanemoto, M. Oshima and I. Isa, Self-healing characteristics of solid electrolytic capacitor with polypyrrole electrolyte, Electrochemistry, 1999, 67, 855 M. Mastragostino, R. Paraventi and A. Zanelli, Supercapacitors based on composite polymer electrodes, J. Electrochem. Soc., 2000,147, 3167. 

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