Electrode , oxide

Mari suggests using oxides as electrode materials33 in oxygen sensors because 

As in the case of metal electrodes, the nature of the charge-transfer reaction for oxide electrodes is a complex function of electrode morphology, overpotential and other conditions. 

An early use of oxygen-ion conducting solid electrolytes was in potentiometric devices for the measurement of oxygen partial pressure. In Section 2 it was shown that the e.m.f. of the cell relates the oxygen partial pressures on both sides through the Nemst equation. 

This equation relies on the assumption that adsorbed oxygen on the electrode surfaces is in equilibrium with gas phase oxygen. This has lead to a number of applications of this type of cell as a sensor. The principle applications are listed below  

In the case where one of the electrodes is exposed to a reacting gas mixture this no longer need be true and the e.m.f. of the cell becomes a reflection of the thermodynamic activity of oxygen adsorbed on the electrode in question,  

Nonetheless, MnCh-based electrodes possess lower specific capacitance and electronic conductivity in addition to a narrower potential window in comparison with their Ru02-based counterparts. Many recent research studies have concentrated on novel synthesis methods for preparation of MnC 2 with various crystal structures, morphologies, and architectures to improve the capacitive behavior. 

There are two theories developed to explain the processes for charge storage in MnC 2.197 One theory suggests that proton (H+) and alkali metal cations (C+), present in the electrolyte, can be reversibly intercalated into the bulk of Mn02 through a reduction reaction and deintercalated via an oxidation reaction 198 

The other theory is based on surface electrosorption of cations on Mn02 according to the following reaction 199 

For both cases, a reversible redox reaction between Mn+4 and Mn+3 occurs to maintain the electroneutrality of the electrode material. 

Manganese oxide can be anodically deposited on various conductive substrates from aqueous solutions containing simple or chelated Mn salts with or without buffers and surfactants. 

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Ion Removal and Metal Oxide Electrodes. The ethylenediamine ( )-functional silane, shown in Table 3 (No. 5), has been studied extensively as a sdylating agent on siUca gel to preconcentrate polyvalent anions and cations from dilute aqueous solutions (26,27). Numerous other chelate-functional silanes have been immobilized on siUca gel, controUed-pore glass, and fiber glass for removal of metal ions from solution (28,29). 

Metal oxide electrodes have been coated with a monolayer of this same diaminosilane (Table 3, No. 5) by contacting the electrodes with a benzene solution of the silane at room temperature (30). Electroactive moieties attached to such silane-treated electrodes undergo electron-transfer reactions with the underlying metal oxide (31). Dye molecules attached to sdylated electrodes absorb light coincident with the absorption spectmm of the dye, which is a first step toward simple production of photoelectrochemical devices (32) (see Photovoltaic cells). 

Electrodes. A number of different types of nickel oxide electrodes have been used. The term nickel oxide is common usage for the active materials that are actually hydrated hydroxides at nickel oxidation state 2+, in the discharged condition, and nickel oxide hydroxide [12026-04-9] NiO OH, nickel oxidation state 3+, in the charged condition. Nickelous hydroxide [12034-48-7J, Ni(OH)2, can be precipitated from acidic solutions of bivalent nickel... 

Because the sdv er oxide electrode is slightly soluble in the potassium hydroxide electroltye the separator is of a barrier type to minimize silver... 

A signihcant problem in tire combination of solid electrolytes with oxide electrodes arises from the difference in thermal expansion coefficients of the materials, leading to rupture of tire electrode/electrolyte interface when the fuel cell is, inevitably, subject to temperature cycles. Insufficient experimental data are available for most of tire elecuolytes and the perovskites as a function of temperature and oxygen partial pressure, which determines the stoichiometty of the perovskites, to make a quantitative assessment at the present time, and mostly decisions must be made from direct experiment. However, Steele (loc. cit.) observes that tire electrode Lao.eSro.rCoo.aFeo.sOs-j functions well in combination widr a ceria-gadolinia electrolyte since botlr have closely similar thermal expansion coefficients. 

To exploit the energy produced in this reaction, the half reactions are separated. The oxidation reaction is carried out at a zinc electrode (Zn Zir + 2 electrons) and the reduction reaction is carried out at a copper electrode (Cu"" + 2 electrons Cu metal). Electrons flow through a metal wire from the oxidizing electrode (anode) to the reducing electrode (cathode), creating electric current that can be harnessed, for example, to light a tungsten bulb. 

Figure 39. Cycling performance of various manganese oxide electrodes.

Sometimes two discharge voltage plateaus are seen on nickel oxide electrodes. Early observations are documented in previous reviews [2, 9]. Normally, nickel oxide electrodes have a voltage plateau on discharge in the potential range of 0.25-0.35V vs. Hg/HgO. The second plateau, which in some cases can account for up to 50% of the capacity, occurs at -0.1 to - 0.6 V. At present there is a general consensus that this second plateau is not due to the presence of a new, less-active, compound [91-94]. Five interfaces have been identified for a discharging NiOOH electrode [93]. These are... 

Oxygen evolution occurs on nickel oxide electrodes throughout charge, on overcharge, and on standby. It is the anodic process in the self-discharge reaction of the positive electrode in nickel-cadmium cells. Early work in the field has been reviewed [9], No significant new work has been reported in recent years. 

Recent advances in fabricating novel metal oxide electrodes have been made by exploiting hydrothermal preparation techniques [93, 94], An example is... 

It is interesting to note that the recently announced Fujifilm development of convertible oxide electrodes results in the formation of a microstructure containing fine dispersions of both Li-Sn alloys and Li20. The latter is known to be a lithiumtransporting solid electrolyte. Thus these electrodes can be thought of as having a... 

G. Foti, D. Gandini, and C. Comninellis, Anodic oxidation of organics on thermally prepared oxide electrodes, Current Topics in Electrochemistry 5, 71-91 (1997). 

Table 3.2. Electrode potentials of zero charge of metal oxide electrodes in contact with electrolyte solutions. )...

The total capacity of a ruthenium oxide electrode [the usual double-layer capacity plus the pseudocapacity of reaction (21.4)] is rather high (i.e., several hundred F/g), even more than at the electrodes of carbon double-layer capacitors. The maximum working voltage of ruthenium oxide pseudocapacitors is about 1.4 V. 

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