Electrochemical activity composites

The optimization of the biorecognition layer by the modification of a transducer used. Nanostmctured poly aniline composite comprising Prussian Blue or poly-ionic polymers has been synthesized and successfully used in the assembly of cholinesterase sensors. In comparison with non-modified sensors, this improved signal selectivity toward electrochemically active species and decreased the detection limits of Chloropyrifos-Methyl and Methyl-Pai athion down to 10 and 3 ppb, respectively. 

Explain clearly how SECM images the microdistribution of the electrochemical activity of composite electrode materials. 

Composite electrodes made of two carbon components were evaluated experimentally as anodes for Li-ion batteries. The electrochemical activity of these electrodes in the reaction of reversible lithium intercalation ffom/to a solution of LiPF6 in ethyl carbonate and diethyl carbonate was studied. Compositions of the electrode material promising for the usage in Li-ion batteries were found. 

With regard to biosensor applications, a wide variety of electrochemically active species (ferrocene, ruthenium complexes, or carbon and metal (Pt, Pd, Au...) [185,186] were also introduced into the sol-gel matrices or adsorbed to improve the electron transfer from the biomolecules to the conductive support [187,188]. For instance, glucose oxidase has been trapped in organically modified sol-gel chitosan composite with adsorbed ferrocene to construct a low-cost biosensor exhibiting high sensitivity and good stability [189]. 

Figure 3.5 [36], For the 02 reduction reaction on freshly prepared LSM electrodes, the initial polarization losses are very high and decrease significantly with the cathodic polarization/current passage (see Figure 3.5b). Consistent with the polarization potential, the impedance responses at open circuit decrease rapidly with the application of the cathodic current passage. For example, the initial electrode polarization resistance, RE, is 6.2 Qcm2 and after cathodic current treatment for 15 min RK is reduced to 0.7 Qcm2 see Figure 3.5 (a). The reduction in the electrode polarization resistance is substantial. The analysis of the impedance responses as a function of the cathodic current passage indicates that the effect of the cathodic polarization is primarily on the reduction in the low-frequency impedance [10]. Such activation effect of cathodic polarization/current on the electrochemical activity of the cathodes was also reported on LSM/YSZ composite electrodes [56-58], Nevertheless, the magnitude of the activation effect on the composite electrodes is relatively small.

The electrochemical performance of La,.6Sr0 4Coo.2Feo.803 (LSCF6428) composition was characterized by Esquirol et al. [102], At 600°C, the conductivity of a porous LSCF coating with thickness of 10 pm was 52.8 and 29.2 Scm 1 when sintered at 1000 and 850°C, respectively. This conductivity is considerably lower than the conductivity values for dense LSCF (300 to 400 Scm-1)- The electrode polarization resistance of LSCF sintered at 850°C was 7.5, 0.23, and 0.03 ohm cm2 at 502, 650, and 801°C, respectively, lower than the electrode polarization resistance values at the same temperatures for the LSCF cathode sintered at 1000°C. The results show that the electrochemical activity of the LSCF electrode for the 02 reduction at... 

The addition of an ionic conductive phase, such as GDC, also promotes the elec-trocatalytic activity of an MIEC cathode. Hwang et al. [108] studied the electrochemical activity of LSCF6428/GDC composites for the 02 reduction and found that the activation energy decreased from 142 kJmol-1 for the pure LSCF electrode to 122 kJmol1 for the LSCF/GDC composite electrodes. Thus, the promotion effect of the GDC is most effective at low-operation temperatures (Figure 3.12). This is due to the high ionic conductivity of the GDC phase at reduced temperatures. 

Similarly, in the development of solid oxide fuel cells (SOFCs), it is well recognized that the microstructures of the component layers of the fuel cells have a tremendous influence on the properties of the components and on the performance of the fuel cells, beyond the influence of the component material compositions alone. For example, large electrochemically active surface areas are required to obtain a high performance from fuel cell electrodes, while a dense, defect-free electrolyte layer is needed to achieve high efficiency of fuel utilization and to prevent crossover and combustion of fuel. 

MIEC with an additional ionically conductive phase, such as GDC or SDC, typically extends the electrochemically active region still further due to the higher ionic conductivity of GDC and SDC compared to that of the perovskites. The optimal composition of a two-phase composite depends in part on the operation temperature, due to the larger dependence of ionic conductivity on temperature compared to electronic conductivity. A two-phase composite of LSCF-GDC therefore has an increasingly large optimal GDC content as the operating temperature is reduced [14], A minimum cathode Rp for temperatures above approximately 650°C has been found for 70-30 wt% LSCF-GDC composite cathodes, while at lower temperatures, a 50-50 wt% LSCF-SDC composite cathode was found to have a lower Rp [15]. 

SOFC electrodes are commonly produced in two layers an anode or cathode functional layer (AFL or CFL), and a current collector layer that can also serve as a mechanical or structural support layer or gas diffusion layer. The support layer is often an anode composite plate for planar SOFCs and a cathode composite tube for tubular SOFCs. Typically the functional layers are produced with a higher surface area and finer microstructure to maximize the electrochemical activity of the layer nearest the electrolyte where the reaction takes place. A coarser structure is generally used near the electrode surface in contact with the current collector or interconnect to allow more rapid diffusion of reactant gases to, and product gases from, the reaction sites. A typical microstructure of an SOFC cross-section showing both an anode support layer and an AFL is shown in Figure 6.4 [24],... 

Song HS, Kim WH, Hyun SH, and Moon J. Influences of starting particulate materials on micro structural evolution and electrochemical activity of LSM-YSZ composite cathode for SOFC. J. Electroceram. 2006 17 759-764. 

In this chapter, two carbon-supported PtSn catalysts with core-shell nanostructure were designed and prepared to explore the effect of the nanostructure of PtSn nanoparticles on the performance of ethanol electro-oxidation. The physical (XRD, TEM, EDX, XPS) characterization was carried out to clarify the microstructure, the composition, and the chemical environment of nanoparticles. The electrochemical characterization, including cyclic voltammetry, chronoamperometry, of the two PtSn/C catalysts was conducted to characterize the electrochemical activities to ethanol oxidation. Finally, the performances of DEFCs with PtSn/C anode catalysts were tested. The microstmc-ture and composition of PtSn catalysts were correlated with their performance for ethanol electrooxidation. 

The use of porous membranes as templates for electrode structures was pioneered by Martin and coworkers nearly 20 years ago, and this approach has since been extended to include numerous electrode compositions and geometries " and applications beyond energy storage, including sensing and separations. In this approach, chemical and electrochemical routes are used to fill in the cylindrical, uniform, unidirectional pores of a free-standing membrane with electrochemically active materials and... 

Figure 6.33. Trends in Pt surface-area normalized electrochemical activity of various ternary alloy compositions with respect to the electrooxidation of methanol. Activity gains are seen in the order Pt, PtRu, PtRuNi, and PtRuCo (adapted from [69]).

Ahn et al. have developed fibre-based composite electrode structures suitable for oxygen reduction in fuel cell cathodes (containing high electrochemically active surface areas and high void volumes) [22], The impedance data obtained at -450 mV (vs. SCE), in the linear region of the polarization curves, are shown in Figure 6.22. Ohmic, kinetic, and mass transfer resistances were determined by fitting the impedance spectra with an appropriate equivalent circuit model. 

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