Structure positive electrodes

Fig. 5.18. Measurement and simulation of a bulk heterojunction solar cell in the dark (a) and under illumination (b). The dark I/V characteristics are plotted semi-logarithmically, whilst the illuminated characteristics are plotted on a linear scale. The bulk heterojunction was simulated as a diode with the following structure positive electrode/p++/i/n++/negative electrode, (c) Local variation of the energy levels (top) and of the carrier densities for a bulk heterojunction solar cell with balanced mobilities, (d) Local variation of the energy levels (top) and of the carrier densities for a bulk heterojunction solar cell with higher electron mobility...

These batteries incorporate a polyacenic semiconductor (PAS) for the active material of the positive electrode, lithium for that of the negative electrode and an organic solvent for the electrolyte. PAS is essentially amorphous with a rather loose structure of molecular-size order with an interlayer distance of 4.0 A, which is larger than the 3.35 A of graphite [56, 57]. 

Basic sulfates are important intermediates during the manufacturing process, since they determine the structure of the active material in the positive electrode, which again is decisive with respect to the... 

A carbon rod is used as a current collector for the positive electrode in dry cells. It is made by heating an extruded mixture of carbon (petroleum coke, graphite) and pitch which serves as a binder. A heat treatment at temperatures of about 1100 °C is used to carbonize the pitch and to produce a solid structure with low resistance. For example, Takahashi [23] reported that heat treatment reduced the specific resistance from 1 Q cm to 3.6xlO"1Qcm and the density increased from 1.7 to 2.02 gem- 1. Fischer and Wissler [24] derived an experimental relationship [Eq. (1)] between the electrical conductivity, compaction pressure, and properties of graphite powder ... 

The compound LiCo02 is an attractive positive electrode for lithium-ion cells because it has a stable structure which is easy to prepare with the ideal layered configuration (da ratio = 4.99). At present, LiCo02 is the preferred positive electrode... 

Solid-state electronic devices such as diodes, transistors, and integrated circuits contain p-n junctions in which a p-type semiconductor is in contact with an n-type semiconductor (Fig. 3.47). The structure of a p-n junction allows an electric current to flow in only one direction. When the electrode attached to the p-type semiconductor has a negative charge, the holes in the p-type semiconductor are attracted to it, the electrons in the n-type semiconductor are attracted to the other (positive) electrode, and current does not flow. When the polarity is reversed, with the negative electrode attached to the n-type semiconductor, electrons flow from the n-type semiconductor through the p-type semiconductor toward the positive electrode. 

Apart from the work toward practical lithium batteries, two new areas of theoretical electrochemistry research were initiated in this context. The first is the mechanism of passivation of highly active metals (such as lithium) in solutions involving organic solvents and strong inorganic oxidizers (such as thionyl chloride). The creation of lithium power sources has only been possible because of the specific character of lithium passivation. The second area is the thermodynamics, mechanism, and kinetics of electrochemical incorporation (intercalation and deintercalation) of various ions into matrix structures of various solid compounds. In most lithium power sources, such processes occur at the positive electrode, but in some of them they occur at the negative electrode as well. 

Figure 7 shows SNIFTIRS spectra for isoquinoline molecules adsorbed on mercury. The reference spectrum in each case was obtained at 0.0V vs. a SCE reference electrode at this potential the molecules are believed to be oriented flat on the metal surface. The vibrational frequencies of the band structure (positive values of absorbance) are easily assigned since they are essentially the same as those reported by Wait et al. (22) for pure isoquinoline. The differences in the spectra are that the bands for the adsorbed species exhibit blue shifting of 3-4 cm" relative to those of the neat material, and the relative intensities of the bands for the adsorbed species are markedly changed. 

The positive electrode should have a porous structure to support the transport of 02 to the electrolyte/electrode interface as much as possible through the gas phase rather than by the slower diffusion in the electrolyte. CNT materials with mesopores and space between the entangled CNTs have been tested as electrode materials for Li-... 

The focus of this paper is on the role electronic structure plays in determining the site preference and mobility of 3d transition-metal ions in an oxide and how these factors in turn affect the resistance of metastable 3d transition-metal oxides against transformation. This is a relevant topic to the Li rechargeable battery field because 3d transition-metal oxides are often used as positive electrode materials. 

In the lithium-ion secondary battery, which was put on the market in 1990, the difficulty of the Li+/Li electrode was avoided by use of a carbon negative electrode Cy), which works as a host for Li+ ions by intercalation. The active material for the positive electrode is typically LiCo02, which is layer-structured and also works as a host for Li+ ions. The electrolyte solutions are nearly the same as those used in the primary lithium batteries. A schematic diagram of a lithium-ion battery is shown in Fig. 12.2. The cell reaction is as follows ... 

An important feature of the positive electrode discharge concerns the nature of the PbS04 deposit since the formation of dense, coherent layers can lead to rapid electrode passivation. Lead dioxide exists in two crystalline forms, rhombic (a-) and tetragonal (/3-), both of which are present in freshly formed electrode structures. Since PbS04 and a-Pb02 are iso morphic, crystals of lead dioxide of this modification tend to become rapidly covered and isolated by lead sulphate, and their utilization is less... 

FIGURE 3.48 The structure of a p-n junction allows an electric current to flow in only one direction, (a) In reverse bias, the negative electrode is attached to the p-type semiconductor the holes in the p-type semiconductor are attracted to the negative electrode, the electrons in the n-type semiconductor are attracted to the positive electrode and current does not flow. 

Another simplification of the model, widely used when modelling SOFC operation, is to consider the Positive electrode/Electrolyte/Negative electrode (PEN), as a lumped structure. Figure 3. 4 shows a schematic representation of a planar SOFC, when the PEN structure is considered in a ID domain. 

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