Membrane oxygen electrode

Choi [59] l-Lactate Dairy products L-Lactate oxidase/with chitosan in an eggshell membrane Oxygen electrode -... 

Mitsubayashi et al. [89] Trimethylamine Mackerel Flavin-containing monooxygenase type-3 (FM03)/in polyvinyl alcohol membrane containing stilbazolium groups. Covered with a Nylon membrane Oxygen electrode ... 

Shin et al. [90] Octopine Scallop Octopine dehydrogenase (ODH)/ODH-bonded beads were packed into a polypropylene reactor tube/ pyruvate oxidase/in a cellulose triacetate, glutaraldehyde and 1,8-diamino-4-aminomethyl octane membrane Oxygen electrode ... 

Chen and Su [102] L-Glutamate L-Glutamic acid fermentation L-Glutamate oxidase/ onto a cellulose triacetate membrane Oxygen electrode ... 

The use of a membrane oxygen electrode for monitoring the oxoacidic properties of molten silicates is described by Perkins [132], Itoh and Yokokawa [133] examined the basicity of silicate melts of the Na20-Al203-Si02 system by the e.m.f. method in cells with the liquid junction, the oxoacidic properties of A1203 were shown to be weaker than those of Si02. 

Cherginets and B anile reported a study of the acidic properties of WO3 by the potentiometric titration method using a gas membrane oxygen electrode Pt(02)lYSZ [142], The addition of WO3 to the molten KC1-NaCl equimolar mixture was accompanied by evaporation of WO2CI2 from the melt... 

Banik [166, 167]. The acidic properties of Na2B407 were studied by the potentiometric titration method using NaOH and Na2C03 as base-titrants, and the equilibrium oxide ion molality was detected by the potentiometric cells with the membrane oxygen electrode Pt(02)lYSZ. The process of titration was performed both from the acid to the base and from the base to the acid. The most characteristic potentiometric curves and the dependencies of the ligand number on the titrant molality are presented in Fig. 1.2.13. 

Rybkin and Seredenko reported the construction of empirical scales of oxoacidity (acidity rows) in molten KC1 at 800 °C and Csl at 650 °C [62, 63]. Estimation of the oxoacidic properties was performed for buffer solutions obtained by the addition of equimolar quantities of conjugated acid and base in the melt. E.m.f. (pO) measurements were performed in the potentiometric cell with the use of a membrane oxygen electrode Pt(02)lYSZ. 

Fig. 1.3.2. Dependence of e.m.f. of the potentoimetric cell with the membrane oxygen electrode against pO in the molten CaCl2-KCl equmilar mixture at 700 °C. The onset of the plateau is connected with CaO precipitation.

The electrochemical processes taking place at a membrane oxygen electrode can be divided into two stages. The first of them is the electrode process itself either the reduction of gaseous oxygen at the metal surface or the reduction of a metal oxide according to such an equation ... 

The second process is the transfer of the formed oxide ion through the solid electrolyte membrane. The potentiometric cells with membrane oxygen electrodes should be characterized by the slope of the E-pO plot equal to 1.15RT/F if the electrode processes correspond to equations (2.4.3) and (2.4.8). The transport number of O2- ions is an important criterion of the membrane electrode reversibility—for good solid electrolytes it is close to unity (1). 

Membrane oxygen electrodes are the most convenient oxide-ion sensors for measurements of ionic melt basicity, since their use is not connected to pollution by foreign admixtures of the melt studied, or with passing gaseous oxygen through the melt. This excludes the drawbacks that are characteristic of other kinds of oxygen electrodes. 

However, the properties of solid electrolytes of which the membranes are made, impose some limitations on the temperature range where the membrane oxygen electrode can be used. Perfil ev and Fadeev determined the lower threshold temperature for the reversible operation of the solid electrolyte membrane to be close to 500 °C [211], owing to oxide-ion conductivity of the membrane. At higher temperatures, the membrane oxygen electrode is considered to be reversible to oxide ions, although the transport number of oxide ions, e.g. in YSZ, achieves the value of unity (1) at temperatures of the order of 1000 °C, i.e. its conductivity becomes completely ionic. 

Fig. 2.4.4. E-pO plots obtained in the calibration of a membrane oxygen electrode Pt(02)lYSZ in the KCl-LiCl eutectice melt at 600 °C 1,2, dependences obtained in argon atmosphere and 3, plot obtained in C02 atmosphere.

Landresse and Duyckaerts reported the results of a potentiometric investigation of the membrane oxygen electrode NilNiOlYSZ in the KCl-LiCl eutectic at 660 °C [231]. The slope of the -pO calibration plot is approximately equal to. 5RTIF. The results of this study were used to estimate the solubility product of uranium oxide in the chloride melt. 

The e.m.f. values of the cell with the membrane oxygen electrode (2.4.25) are positive, which corresponds to the running of the following potentialdefining process in the cell... 

The reversibility of the Pt(02)lYSZ membrane oxygen electrode with respect to oxide ions was examined at 600, 700 and 800 °C, with KOH being... 

The E-pO plot of the cell with the gas membrane oxygen electrode at 600 °C is presented in Fig. 2.4.4, sections 1 and 2 [187], This plot contains an inflection point at pO 2, which is characteristic of such membrane electrodes. The positive e.m.f. values of the cell (2.4.28) correspond to running the following potential-determining reaction ... 

Thus, the presence of the inflection point in the calibration E-pO plots is a distinctive feature of the work on the gas membrane oxygen electrode in high-temperature ionic melts. More exactly, there are two linear sections, with slopes corresponding to values of z equal to 1 and 2. This result, noted at first in our paper [233], showed that the electrode process at the gas membrane oxygen electrode was essentially dependent not on peculiarities of the assumed potential-determining process with the participation of the given Lux base (as was considered before), but on the equilibrium concentration of oxide ion created by dissociation of this base in the ionic melt. 

The described behaviour of the gas membrane oxygen electrode agrees qualitatively with the work on conventional gas oxygen electrodes in the nitrate melts considered above at different concentrations of oxide ions. 

Fig. 2.4.7. Schematic diagram of work of gas membrane oxygen electrode Pt(02)lYSZ.

Hence, the character of the reversibility of membrane oxygen electrodes with respect to oxide ions in ionic melts is dependent on the shift of the... 

The behaviour of a Pt(02)lYSZ membrane oxygen electrode at 700 °C was studied in Refs. [162, 189]. The calibration E-pO plots obtained, one of which is presented in Fig. 2.4.8, clearly demonstrate the drawbacks of the direct calibration method at low initial molalities of oxide ions. 

Fig. 2.4.8. Calibration -pO plot for potentiometric cell (2.4.28) with a membrane oxygen electrode in the KCl-LiCl eutectic melt at 700 °C 1, the section where the effect of oxygen admixtures is predominant 2, section with 3, section with z = 1.

The calibration plot for the membrane oxygen electrode at 800 °C has no characteristic features, in contrast with similar plots obtained at 600 and 700 °C the inflection point is located at pO 2 and the slope at low pO values is appreciably less than 2.3RT/F. The latter fact is seemingly caused by the elevated acidity of the Li+-containing melt in comparison, for example, with the KCl-NaCl equimolar mixture. 

The reversibility of the Pt(02)IZr02(Ca0) membrane oxygen electrode in molten KCl-NaCl has been studied in a number of works. Thus, the authors of Refs. [65, 236, 237] reported the application of the electrode with a Zr02(CaO) solid electrolyte membrane for the potentiometric investigation of some heterogeneous acid-base equilibria and the construction of the row of cation acidity in the KCl-NaCl melt. 

The calibration of a potentiometric cell with the Pt(02) membrane electrode with the use of KOH, in the range of pO values from 1 to 4, results in a slope value of 0.0995 V [236]. However, a Pt(02)IZr02(Ca0) gas membrane oxygen electrode should exhibit the peroxide function in the stated pO range, and, therefore, the correctness of the data presented is very doubtful. 

The potentiometric investigations of the Pt(02)lYSZ membrane oxygen electrode at 700 and 800 °C by the calibration using various Lux bases have been reported in some of our papers. The potentiometric cell used for the studies in the molten KCl-NaCl eutectic consisted of the oxygen electrode of the type under study and the silver reference one [233]. The oxide-ion donors... 

Fig. 2.4.11. The limits of reversible work of the membrane oxygen electrodes in chloride melts (KCl-NaCl eutectic) melt at 1000 K (pO values expressed in molar fractions), by R. Combes, J.

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