Electrolytes oxide

Fully stabilized zirconias doped with Y2O3 (8-9 mol%) or CaO (15 mol%), or partially stabilized zirconia doped with MgO (3 mol%), are the most widely used electrolytes in devices operating at temperatures higher than 800-850 °C. 

For temperatures less than 800 °C, a variety of ceramic materials have been 

One promising group of solid electrolytes are the apatite-type silicates Aio x (SiO4)6O2 8 (where A = rare- and alkaline-earth cations). These exhibit a high ionic transport number, a moderate thermal expansion, and show no chemical reactivity with the cathode materials [41]. 

---

In low temperature fuel ceUs, ie, AEG, PAEC, PEEC, protons or hydroxyl ions are the principal charge carriers in the electrolyte, whereas in the high temperature fuel ceUs, ie, MCEC, SOEC, carbonate and oxide ions ate the charge carriers in the molten carbonate and soHd oxide electrolytes, respectively. Euel ceUs that use zitconia-based soHd oxide electrolytes must operate at about 1000°C because the transport rate of oxygen ions in the soHd oxide is adequate for practical appHcations only at such high temperatures. Another option is to use extremely thin soHd oxide electrolytes to minimize the ohmic losses. 

Electrolytic Oxidation. Electrolytic oxidation of ferromanganese or manganese metal is a one-stage process that circumvents the problem of ore impurities. Moreover, this procedure can be used with low caustic concentrations at room temperature. This process is based on the following... 

Smooth oxidized electrolytic iron 260-980 0.78-0.82 Oxidized by heating at 750 F. 750 0.11... 

Similarly if tlris electrolyte is made into a composite with SrS, SrC2 or SrH2, the system may be used to measure sulphur, carbon and hydrogen potentials respectively, tire latter two over a resuicted temperamre range where the carbide or hydride are stable. The advantage of tlrese systems over the oxide electrolytes is that the conductivity of the fluoride, which conducts by F ion migration, is considerably higher. 

Solid oxide fuel cells consist of solid electrolytes held between metallic or oxide elecU odes. The most successful fuel cell utilizing an oxide electrolyte to date employs Zr02 containing a few mole per cent of yttrium oxide, which operates in tire temperature range 1100-1300 K. Other electrolytes based... 

Electrochemistry plays an important role in the large domain of. sensors, especially for gas analysis, that turn the chemical concentration of a gas component into an electrical signal. The longest-established sensors of this kind depend on superionic conductors, notably stabilised zirconia. The most important is probably the oxygen sensor used for analysing automobile exhaust gases (Figure 11.10). The space on one side of a solid-oxide electrolyte is filled with the gas to be analysed, the other side... 

The overall pattern of behaviour of titanium in aqueous environments is perhaps best understood by consideration of the electrochemical characteristics of the metal/oxide and oxide-electrolyte system. The thermodynamic stability of oxides is dependent upon the electrical potential between the metal and the solution and the pH (see Section 1.4). The Ti/HjO system has been considered by Pourbaix". The thermodynamic stability of an... 

Electron transfer rate and its exponential increase at zinc oxide-electrolyte interfaces, 512 Electronic conductivity... 

T.I. Politova, G.G. Gal vita, V.D. Belyaev, and V.A. Sobyanin, Non-Faradaic catalysis the case of CO oxidation over Ag-Pd electrode in a solid oxide electrolyte cell, Catal. Lett. 44, 75-81 (1997). 

V.A. Sobyanin, V.I. Sobolev, V.D. Belyaev, O.A. Mar ina, A.K. Demin, and A.S. Lipilin, On the origin of the Non-Faradaic electrochemical modification of catalytic activity (NEMCA) phenomena. Oxygen isotope exchange on Pt electrode in cell with solid oxide electrolyte, Catal. Lett. 18, 153-164 (1993). 

The starting material for all industrial chlorine chemistry is sodium chloride, obtained primarily by evaporation of seawater. The chloride ion is highly stable and must be oxidized electrolytically to produce chlorine gas. This is carried out on an industrial scale using the chlor-alkali process, which is shown schematically in Figure 21-15. The electrochemistry involved in the chlor-alkali process is discussed in Section 19-. As with all electrolytic processes, the energy costs are very high, but the process is economically feasible because it generates three commercially valuable products H2 gas, aqueous NaOH, and CI2 gas. 

Park CW, Ryu HS, Kim KW, Ahn JH, Lee JY, Ahn HJ (2007) Discharge properties of all-solid sodium-sulfur battery using poly (ethylene oxide) electrolyte. J Power Sources 165 450-454... 

Solid-oxide electrolytes are natural choices for oxygen transport since they transfer oxide ions directly ... 

With these solid-oxide electrolytes, designed to operate in relatively 02-rich feed (e.g. air), gas-diffusion electrodes with their enhanced contact area, are not necessary, and electrode materials can be applied directly onto the electrolyte surfaces in thin films. 

Various mechanisms for electret effect formation in anodic oxides have been proposed. Lobushkin and co-workers241,242 assumed that it is caused by electrons captured at deep trap levels in oxides. This point of view was supported by Zudov and Zudova.244,250 Mikho and Koleboshin272 postulated that the surface charge of anodic oxides is caused by dissociation of water molecules at the oxide-electrolyte interface and absorption of OH groups. This mechanism was put forward to explain the restoration of the electret effect by UV irradiation of depolarized samples. Parkhutik and Shershulskii62 assumed that the electret effect is caused by the accumulation of incorporated anions into the growing oxide. They based their conclusions on measurements of the kinetics of Us accumulation in anodic oxides and comparative analyses of the kinetics of chemical composition variation of growing oxides. 

There are a number of papers offering explanations of the breakdown phenomenon. Suggestions have been made that it is due to the presence of macro- and microdefects in oxides (electrolyte-filled fissures, micropores, flaws, etc.).286 Joule heating effects were also considered289 as well as volume increase and the resulting increase of internal stresses during anodization,290 elec-trostriction effects,291 or field-assisted ionic migration.292... 

Melendres et ai (1991) reported the in-situ study of the electrode/oxide and oxide/electrolyte interfaces for a copper electrode in pH 8.4 borate buffer under potential control. The grazing-angle incidence arrangement employed by the authors is shown in Figure 2.81(a) and a cyclic voltammogram of the Cu electrode in the buffer is shown in Figure 2.81(b). 

Four solid oxide electrolyte systems have been studied in detail and used as oxygen sensors. These are based on the oxides zirconia, thoria, ceria and bismuth oxide. In all of these oxides a high oxide ion conductivity could be obtained by the dissolution of aliovalent cations, accompanied by the introduction of oxide ion vacancies. The addition of CaO or Y2O3 to zirconia not only increases the electrical conductivity, but also stabilizes the fluorite structure, which is unstable with respect to the tetragonal structure at temperatures below 1660 K. The tetragonal structure transforms to the low temperature monoclinic structure below about 1400 K and it is because of this transformation that the pure oxide is mechanically unstable, and usually shatters on cooling. The addition of CaO stabilizes the fluorite structure at all temperatures, and because this removes the mechanical instability the material is described as stabilized zirconia (Figure 7.2). 

Hatch well CE, Sammes NM, Tompsett GA, and Brown IWM. Chemical compatibility of chromium-based interconnect related materials with doped cerium oxide electrolyte. J. Eur. Ceram. Soc. 1999 19 1697-1703. 

Comparison between the polarized electrode-electrolyte interface and the reversible (Al203) oxide-electrolyte interface. Surface tension (interfacial) tension, charge density and differential capacity, respectively, are plotted as a function of the rational potential vy (at pzc vy is set = 0) in the case of Hg and as a function of ApH (pH-pH ) in the case of Al203 (pH = pHpzc when a = 0). 

Surface complexation models for the oxide-electrolyte interface are reviewed two models for surface hydrolysis reactions are considered (diprotic surface groups and monoprotic surface groups) and four models for the electric double layer (Helmholtz,... 

Any complete mechanistic description of chemical reactions at the oxide-aqueous electrolyte interface must include a description of the electrical double layer. While this fact has been recognized for years, a satisfactory description of the double layer at the oxide-electrolyte interface still does not exist. 

Another fundamental problem encountered in characterizing reactions at the oxide-electrolyte interface is the coupling between electrostatic and chemical interactions, which makes it difficult to distinguish the effects of one from the effects of the other. 

Westall and Hohl (2) have shown that many models for reactions at the oxide-electrolyte interface are indeterminate in this regard. 

Many of the studies, from which our current understanding of reactions at the oxide-electrolyte interface has developed, were based on titrations of colloidal suspensions of oxides. The key to resolving questions left open by this work lies in the study of better defined oxide surfaces, the examination of a particular interface by many different experimental methods, and the development of mathematical methods for interpreting the data. 

---