Oxygen solid electrolytes

The development of novel oxygen solid electrolytes conducting at temperatures below 800 °C is of major importance in the large-scale development of applications. 

Vashook V, Zosel J, Guth U (2012) Oxygen solid electrolyte coulometry (OSEC). J Solid State Electrochem 16 3401-3421... 

Fig.1 Schematic presentation of oxygen solid electrolyte coulometry method (OSEC)...

Oxygen solid electrolyte coulometry can be successfully used for the following ... 

Oxygen Solid Electrolyte Coulometry, Fig. 2 Schematic representation of the cells for coulometric experiments SE solid electrolyte tube, U i potential electrodes, 7 current electrodes, S sample, HTG high temperature glass... 

Oxygen Solid Electrolyte Coulometry in Quasi-Closed Systems... 

Oxygen solid electrolyte coulometry in quasi-closed systems is understood at first the complete isolation of the material to be investigated in a minimal chamber with gas-dense solid electrolyte wall attached out- and inside with electrochemical active electrodes. Then oxygen can only be admitted to the chamber or removed from it quantitatively by coulometric titration. The chamber can be made completely (Fig. 2) or partly of solid electrolyte material. Current (lei) and potential (Uei) electrodes are insulated from each other with gas-dense high temperature glass (HTG) layer, so titration current and voltage are simultaneously measurable at this construction of the cell. 

Oxygen Solid Electrolyte Coulometry, Fig. 3 Scheme of device for simultaneous in situ solid electrolyte coulometry and electrical conductivity measmement... 

Note that an electrical potential applied, to an oxygen solid electrolyte corresponds to an equivalent modification of the local oxygen activity (Section 7.2.1). The above catal3rtic effect has been termed NEMCA effect (Non-Electrochemical Modification of Catalytic Activity) [477]. 

Figure 5.3 The dependence of the conductivity of typical solid electrolytes on the oxygen pressure, showing the limits of electrolytic behaviour where t o is very close to unity...

In the ceramics field many of the new advanced ceramic oxides have a specially prepared mixture of cations which determines the crystal structure, through the relative sizes of the cations and oxygen ions, and the physical properties through the choice of cations and tlreh oxidation states. These include, for example, solid electrolytes and electrodes for sensors and fuel cells, fenites and garnets for magnetic systems, zirconates and titanates for piezoelectric materials, as well as ceramic superconductors and a number of other substances... 

A unique application of the solid oxygen electrolytes is in dre preparation of mixed oxides from metal vapour deposits. For example, the ceramic superconductors described below, have been prepared from mixtures of the metal vapours in the appropriate proporhons which are deposited on the surface of a solid electrolyte. Oxygen is pumped tluough the electrolyte by the application of a polarizing potential across the electrolyte to provide the oxidant for the metallic layer which is formed. 

Another application is in tire oxidation of vapour mixtures in a chemical vapour transport reaction, the attempt being to coat materials with a tlrin layer of solid electrolyte. For example, a gas phase mixture consisting of the iodides of zirconium and yttrium is oxidized to form a thin layer of ytnia-stabilized zirconia on the surface of an electrode such as one of the lanthanum-snontium doped transition metal perovskites Lai j.Srj.M03 7, which can transmit oxygen as ions and electrons from an isolated volume of oxygen gas. 

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. 

The basic zirconia oxygen sensor design is illustrated in Fig. 13.52, which shows the principle of the zirconia solid oxygen-ion electrolyte. The sensor consists of a closed-end tube of ceramic zirconia ZrO )). The zirconia ceramic... 

Wagner was first to propose the use of solid electrolytes to measure in situ the thermodynamic activity of oxygen on metal catalysts.17 This led to the technique of solid electrolyte potentiometry.18 Huggins, Mason and Giir were the first to use solid electrolyte cells to carry out electrocatalytic reactions such as NO decomposition.19,20 The use of solid electrolyte cells for chemical cogeneration , that is, for the simultaneous production of electrical power and industrial chemicals, was first demonstrated in 1980.21 The first non-Faradaic enhancement in heterogeneous catalysis was reported in 1981 for the case of ethylene epoxidation on Ag electrodes,2 3 but it was only... 

M. Stoukides, and C.G. Vayenas, The effect of electrochemical oxygen pumping on the Rate and Selectivity of Propylene Oxidation on Silver in a Solid Electrolyte Cell, J. Electrochem. Soc. 131(4), 839-845 (1984). 

When a solid electrolyte component is interfaced with two electronically conducting (e.g. metal) films (electrodes) a solid electrolyte galvanic cell is formed (Fig. 3.3). Cells of this type with YSZ solid electrolyte are used as oxygen sensors.8 The potential difference U R that develops spontaneously between the two electrodes (W and R designate working and reference electrode, respectively) is given by ... 

Wagner first proposed the use of such galvanic cells in heterogeneous catalysis, to measure in situ the thermodynamic activity of oxygen O(a) adsorbed on metal electrodes during catalytic reactions.21 This led to the technique of solid electrolyte potentiometry (SEP).22 26... 

E.C. Subbarao, and H.S. Maiti, Solid electrolytes with oxygen ion conduction, Solid State Ionics 11, 317-338 (1984). 

Then let us examine the rate relaxation time constant x, defined as the time required for the rate increase Ar to reach 63% of its steady state value. It is comparable, and this is a general observation, with the parameter 2FNq/I, (Fig. 4.13). This is the time required to form a monolayer of oxygen on a surface with Nq sites when oxygen is supplied in the form of 02 This observation provided the first evidence that NEMCA is due to an electrochemically controlled migration of ionic species from the solid electrolyte onto the catalyst surface,1,4,49 as proven in detail in Chapter 5 (section 5.2), where the same transient is viewed through the use of surface sensitive techniques. 

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