Counterelectrode metals

Figure 7. Measured vibrational energies for hydroxyl and benzoate ions on alumina using (9) optical techniques and (O) IETS for three different counterelectrode metals. The energies measured using IETS are always lower than those measured optically, but the shifts are not large enough to interfere with identification of the modes or to indicate large perturbations of the surface species by the presence of the counterelectrode (19).

Figure 20. Current-voltage curves for various counterelectrode metals [from Standley and Maissel, J. Appl Phys. 35 (1964) 1530].

The photopontential also approaches to zero when the semiconductor photoelectrode is short-circuited to a metal counterelectrode at which a fast reaction (injection of the majority carriers into the electrolyte) takes place. The corresponding photocurrent density is defined as a difference between the current densities under illumination, /light and in the dark, jDARK ... 

Platinum-loaded Ti02 systems can be considered as a short-circuited photo-electrochemical cell where the Ti02 semiconductor electrode and metal Pt counterelectrode are brought into contact [159]. Light irradiation can induce electron-hole (e -h +) pair formation and surface oxidation and also reduction reactions on each Pt/Ti02 particle (Figure 4.11). These powder-based systems lack the advantage of... 

In the case of the scheme of Fig. 9.18 the primary electrode coul l be a thin film of polymethylthiophene ([C5H7S]jj) deposited on ij ITO-coated glass, the electrolyte can be the usual LiClO -PC solution and the counterelectrode lithium metal (Li), to obtain the following structure ... 

In electrochemical etching of metals the plate and a counterelectrode are placed in a liquid electrolyte and a voltage is applied to create an electric field between the plates to dissolve the metal as soluble ions. Discuss the following issues and sketch configurations and profiles. 

Similar photovoltaic cells can be made of semiconductor/liquid junctions. For example, the system could consist of an n-type semiconductor and an inert metal counterelectrode, in contact with an electrolyte solution containing a suitable reversible redox couple. At equilibrium, the electrochemical potential of the redox system in solution is aligned with the Fermi level of the semiconductor. Upon light excitation, the generated holes move toward the Si surface and are consumed for the oxidation of the red species. The charge transfer at the Si/electrolyte interface should account for the width of occupied states in the semiconductor and the range of the energy states in the redox system as represented in Fig. 1. 

The electronic excitation also promotes an electron to the conduction band, where it can function effectively as a reductant at a potenial governed by the position of the conduction band edge. In parallel fashion, reduced products can accumulate at a metal counterelectrode which has collected the photogenerated electrons from the conduction band. 

If a complete cell is charged to, e.g., 4.1 V, then the potential Z carbon of the fully lithiated negative electrode will be about 0.1 V vs. Li/Li+. Therefore, the potential Eoxiie of the fully charged positive electrode in this example will be 4.2 V vs. Li/Li+. Needless to say that this trivial relationship must be remembered when data for half cells (vs. metallic lithium) are compared to the data for complete cells. An important consequence of this trivial relationship is the potential excursion of the counterelectrode in the case of an anomalous behavior of the carbon electrode (and vice versa). Imagine that, in the previous example the potential of the carbon would shift to 0.3 V vs. Li/Li+ due to a malfunction of the carbon electrode. If the end-of-charge voltage of the complete cell would be the same, namely 4.1V, then the potential of the positive electrode would be 4.4 V vs. Li/Li+. In such a case, the safety of the entire cell could be compromised. 

There are studies in which the fact that active metal electrodes are covered with surface films is not so important, e.g., when these metals are used as counterelectrodes, or when they are studied as practical anodes in batteries. However, even in these cases, the native active metals as received may be covered with two thick films. It is therefore, necessary to remove the initial native film covering the active metal under an inert atmosphere. The passivating films of lithium and calcium can be scraped off with a stainless steel knife. In the case of harder active metals such as magnesium and aluminum, an abrasive cloth or... 

In order to create glow discharge in the basket, it is necessary to insert the hot electrode coaxially placed in the center of the basket and ground the reactor and the tumbler basket as the counterelectrodes. Without the hot center electrode, glow discharge will develop between the reactor wall and the metal basket, i.e., in the volume (Fi — F2) outside of the basket, and develop the same situation for the secondary plasma discussed in Chapter 18, which could be good for surface treating... 

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