Electron layered oxides

Fig. 35. Number of electrons for oxidation of an adsorbed molecule of 2,2, 5,5 -tetrahydroxybiph-enyl (THBP) or hydroquinone (HQ). Experimental conditions polycrystalline Pt thin-layer electrode in 1 M HC104 electrolyte at 23 1°C. Reprinted from ref. 73.

Time-dependent measurements, where the transient concentration of ground-state sensitizer that was being formed by the reverse electron transfer from the layered oxide to RuL3 was monitored as a function of time employing reflectance flash photolysis (in the absence of I ), reveal a very slow reverse electron transfer. It is estimated that the process of reverse electron transfer is at least three orders of magnitude slower than the forward transfer. 

Figure 5 Thermodynamic parameters associated with organohaUde reactivity (a) electon accepting species versus redox potential (b) relative importance of oxidation versus dechlorination rates as a function of number of chlorines [1-8] and (c) trend between energy difference of the HOMO and LUMO electron layers and Gibbs free energy of...

The stability of water with respect to oxidation to O2, and reduction to H2, limits the range of electrode potentials and the oxidation states possible in any system containing water. These limits are the dashed lines in Table 4.2. Dissolved F2 and CI2 gases are unstable because of their high electrode potentials. The reduced states F and Cl- are the stable states in water because they have accepted an electron and thereby discharged their oxidizing power. Metals are likewise unstable in water and soils because of their tendency to oxidize, to donate electrons. Then oxidized states (Al3+, Ca2+, K h, etc.) are stable in water. Table 4.2 implies correctly that the common metals are unstable and will corrode. Exceptions such as aluminium and zinc metals are metastable an oxide layer that forms initially on their surfaces inhibits further oxidation. Soils and seawater catalyze the breakdown of these protective layers and speed up their corrosion (oxidation). Iron and steel do not form this protective layer. 

V Transparent electronic conductors are required in certain applications. A thin layer of an electronically conducting oxide deposited on a glass substrate is then used. 

Layered Oxides. Most solid cathode hosts are transition-metal oxides in which Epc lies in either a mixed-valent redox couple or a narrow band of rf-electron states. The Pb02 cathode of the lead-acid battery is an exception its Epc is located in a narrow Pb-6s band well-separated from the broad, empty Pb-6p band because Pb is heavy. 

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