Electrochemical active phase

Manganese dioxide(s), 15 566 battery-active, 15 617-618 electrochemically active phases of, 15 583-584... 

Figure 6.2 Possible pathways of the charge transfer reactions and the charge transport processes proceeding at a three-phase electrode consisting of an electrochemically active Phase II, and electrolyte solution (Phase III), and an electron conductor (Phase I). The electron flux shows the direction in which electrons can be transferred across the interface I/II and...

Properties. Only plattnerite has attractive features for electrochemical applications such as a low electrical resistivity (40 to 50 p 2.cm), a good chemical and electrochemical corrosion resistance in sulfates media even at low pH, and a high overvoltage for the evolution of oxygen in suhuric- and nitric-acid-containing electrolytes while it withstands chlorine evolution in hydrochloric acid. In fact, the more electrochemically active phase consists... 

Designing an alloy/C composite material, in which an electrochemically active phase is homogeneously dispersed within in carbonaceous matrix. The carbonaceous materials are light and possess high electronic conductivity and high Li-ion diffusivity. It is presently a well-studied system. " °... 

Most of the electrochemical promotion studies surveyed in this book have been carried out with active catalyst films deposited on solid electrolytes. These films, typically 1 to 10 pm in thickness, consist of catalyst grains (crystallites) typically 0.1 to 1 pm in diameter. Even a diameter of 0.1 pm corresponds to many (-300) atom diameters, assuming an atomic diameter of 3-10 10 m. This means that the active phase dispersion, Dc, as already discussed in Chapter 11, which expresses the fraction of the active phase atoms which are on the surface, and which for spherical particles can be approximated by ... 

Two cases of electrochemical promotion of commercial catalysts have been very recently reported in the literature and, not too surprisingly, in both cases the active phase was conductive, electronically or ionically. 

The function of the detector in hplc is to monitor the mobile phase emerging from the column. The output of the detector is an electrical signal that is proportional to some property of the mobile phase and/or the solutes. Refractive index, for example, is a property of both the solutes and the mobile phase. A detector that measures such a property is called a bulk property detector. Alternatively, if the property is possessed essentially by the solute, such as absorption of uv/visible radiation or electrochemical activity, the detector is called a solute property detector. Quite a large number of devices, some of them rather complicated and tempremental, have been used as hplc detectors, but only a few have become generally useful, and we will examine five such types. Before doing this, it is helpful to have an idea of the sort of characteristics that are required of a detector. 

Chitosan-clay bio-nanocomposites are very stable materials without significant desorption of the biopolymer when they are treated with aqueous salt solutions for long periods of time. In this way, they act as active phases of electrochemical sensors for detection of ions (Figure 1.8). The particular nanostructuration of the biopolymer in the interlayer region drives the selective uptake of monovalent versus polyvalent anions, which has been applied in electrode arrays of electronic tongues [132]. 

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. 

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]. 

Because the reaction in a CL requires three-phase boundaries (or interfaces) among Nafion (for proton transfer), platinum (for catalysis), and carbon (for electron transfer), as well as reacfanf, an optimized CL structure should balance electrochemical activity, gas transport capability, and effective wafer management. These goals are achieved through modeling simulations and experimental investigations, as well as the interplay between modeling and experimental validation. 

The important processes occurring in a catalyst layer include interfacial ORR at the electrochemically active sites, proton transport in the electrolyte phase, electron conduction in the electronic phase (i.e., Pt/C), and oxygen diffusion through the gas phase, liquid water, and electrolyte phase. 

The optical properties of MPS3 and Li,MPS3 have been studied. The host phases are broad-band semiconductors with band gaps of 1.3-3.5 eV. The three compounds that are electrochemically active are NiPS3, FePS3 and FePSe3, which possess the smallest band gaps. Upon intercalation with lithium, the transmittance decreases until the... 

Randin, in a recently-published paper 44>, investigated solely on the basis of results from the literature the relationship between electrocatalytic activity for 2 reduction on the one hand, and oxidation potential, magnetic moment, and catalytic properties in gas-phase reactions on the other. It was found for the transition-metal phthalocyanines that magnetic moment and activity for the dehydrogenation of cyclohexanedione increase together with the activity of the phthalocyanines for 2 reduction, while the oxidation potential becomes less. The last fact can be seen from Fig. 29, in which the first oxidation potentials in 1-chlomaphthalene, measured by Manassen and Bar-Ilan 45>, are plotted against electrochemical activity. This result shows that the more easily an electron can... 

There are numerous applications that depend on chemically reacting flow in a channel, many of which can be represented accurately using boundary-layer approximations. One important set of applications is chemical vapor deposition in a channel reactor (e.g., Figs. 1.5, 5.1, or 5.6), where both gas-phase and surface chemistry are usually important. Fuel cells often have channels that distribute the fuel and air to the electrochemically active surfaces (e.g., Fig. 1.6). While the flow rates and channel dimensions may be sufficiently small to justify plug-flow models, large systems may require boundary-layer models to represent spatial variations across the channel width. A great variety of catalyst systems use... 

All of the fat-soluble vitamins, including provitamin carotenoids, exhibit some form of electrochemical activity. Both amperometry and coulometry have been applied to electrochemical detection. In amperometric detectors, only a small proportion (usually <20%) of the electroactive solute is reduced or oxidized at the surface of a glassy carbon or similar nonporous electrode in coulometric detectors, the solute is completely reduced or oxidized within the pores of a graphite electrode. The operation of an electrochemical detector requires a semiaqueous or alcoholic mobile phase to support the electrolyte needed to conduct a current. This restricts its use to reverse-phase HPLC (but not NARP) unless the electrolyte is added postcolumn. Electrochemical detection is incompatible with NARP chromatography, because the mobile phase is insufficiently polar to dissolve the electrolyte. A stringent requirement for electrochemical detection is that the solvent delivery system be virtually pulse-free. 

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