Oxygen concentration cell electrodes

Schematically speaking an elementary SOFC is composed of a solid oxide electrolyte, an oxygen electrode (cathode) and a fuel electrode (anode), as shown in Fig. 1. To form a battery, several elementary cells must be connected using an appropriate material. A SOFC may be considered as an oxygen concentration cell [6] of the following type...

In a recent study (4) kinetic measurements in a CSTR were combined with simultaneous in situ measurement of the thermodynamic activity of oxygen adsorbed on the catalyst by using the technique of solid electrolyte potentiometry (SEP). The technique originally proposed by C. Wagner (1) utilizes a solid electrolyte oxygen concentration cell with one electrode also serving as the catalyst for the reaction under study. It has already been used to study the oxidation of ethylene on Ag (5) and on Pt (6). 

Gas sensors — (a) Gas sensors with liquid electrolytes — Figure 2. can regarded as an Oxygen concentration Cell. They Scheme of a potentiometric gas sensor work depending on electrode material in a broad range... 

The SOFC has been wrongly described in the early literature as an oxygen concentration cell. On the contrary, the author asserts that all fuel cells are ion concentration devices. Also that zero external current cell equilibrium equates to an internal balanced state, at which no net ion transfer occurs between electrodes, due to a balance between counter-directed ion migration and diffusion. The SOFC (Mobius and... 

The basic principle of the potentiometric ZrOz oxygen concentration cell is explained in Section 5.63.1, Fig. 5.6.2. The sensor consists of a Zr02 solid electrolyte body coated with two Pt electrodes, a measuring electrode exposed to the exhaust gas with an oxygen partial pressure of p 02, and a reference electrode exposed to a reference atmosphere with a constant oxygen partial pressure of p f2, typically ambient air. 

Consider the exhaust gas analyzer based on the oxygen concentration cell, (2.4.21). The electrode reaction that occurs at high temperature at both of the Pt/Zr02 + Y2O3 interfaces is... 

If one electrode of an oxygen concentration cell is the standard oxygen electrode, then is the electrode potential of the second electrode. With the values of the fundamental constants, the electrode potential equation of the oxygen electrode is given by... 

An electrolytic cell, the electromotive force of which is due to a difference in air (oxygen) concentration at one electrode as compared with that at another electrode of the same material an oxygen concentration cell (a cell resulting from a potential difference caused by different amounts of oxygen dissolved at two locations). 

Differential Aeration Cells. This type of concentration cell is more important in practice than is the salt concentration cell. The cell may be made from two electrodes of the same metal (i.e., iron), immersed completely in dilute sodium chloride solution (Figure 4-433). The electrolyte around one electrode (cathode) is thoroughly aerated by bubbling air. Simultaneously the electrolyte around the other electrode is deaerated by bubbling nitrogen. The difference in oxygen concentration causes a difference in potential. This, in turn, initiates the flow of current. This type of cell exists in several forms. Some of them are as follows [188]. 

No experiments appear to have been made with such cells, although the equation has been verified with oxygen at different partial pressures in admixture with nitrogen, with platinum electrodes and hot solid glass as electrolyte (Haber and Moser). A similar case is that of two amalgams of a metal, of different concentrations, as electrodes, and a solution of a salt of the metal as electrolyte (G. Meyer, 1891). Here we must take the osmotic pressures of the metals in the amalgams, Pi, P2, and, for an 7i-valent metal ... 

The partial oxygen pressure, p02, is particularly significant in metabolic processes of cells, and its variation from normal values often indicates pathologies (ischemic diseases, strokes, tumors). Accurate and localized measurements of the oxygen concentration are also desirable for differentiation between venous and arterial blood, or for cerebral mapping of task activation. In the past, invasive methods were used involving oxygen-sensitive electrodes which had to be placed directly in the blood or tissue and could only offer p02 from a few body points. 

Oxides play many roles in modem electronic technology from insulators which can be used as capacitors, such as the perovskite BaTiOs, to the superconductors, of which the prototype was also a perovskite, Lao.sSro CutT A, where the value of x is a function of the temperature cycle and oxygen pressure which were used in the preparation of the material. Clearly the chemical difference between these two materials is that the capacitor production does not require oxygen partial pressure control as is the case in the superconductor. Intermediate between these extremes of electrical conduction are many semiconducting materials which are used as magnetic ferrites or fuel cell electrodes. The electrical properties of the semiconductors depend on the presence of transition metal ions which can be in two valence states, and the conduction mechanism involves the transfer of electrons or positive holes from one ion to another of the same species. The production problem associated with this behaviour arises from the fact that the relative concentration of each valence state depends on both the temperature and the oxygen partial pressure of the atmosphere. 

The current flowing in the cell will depend upon the rate of diffusion of oxygen to the electrode surface and ultimately on the concentration of oxygen in the external solution. The construction of such an electrode is shown in Figure 6.14. 

OXYGEN CELL. An electrolytic cell whose emf is due to a difference in oxygen concentration at one electrode compared with that at another electrode of the same material. 

To check the electrode response and set zero oxygen concentration, inject 0.5 ml freshly prepared saturated sodium dithionite solution through the hole in the cell plug (the recorder pen should move rapidly toward zero). Use this reading to set the zero baseline. 

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