Pumping, oxygen

M. Stoukides, and C.G. Vayenas, The effect of Electrochemical Oxygen Pumping on the Rate and Selectivity of Ethylene Oxidation on Polycrystalline Silver, J. Catal. 70, 137-146(1981). 

O.A. Mar ina, V.A. Sobyanin, V.D. Belyaev, and V.N. Parmon, The effect of electrochemical oxygen pumping on catalytic properties of Ag and Au electrodes at gas-phase oxidation ofCH4, Catalysis Today 13, 567-570 (1992). 

Oxide ion conductors have found widespread apphcations in our modem society. The devices based on oxide ion conductors include oxygen sensors, solid oxide fuel cells (SOFCs), and oxygen pump. 

Zirconia cells similar to the ones employed in the present study, have been used i) by Mason et al (18) to electrochemically remove oxygen from Pt and Au catalysts used for NO decomposition. It was shown that electrochemical oxygen pumping causes a dramatic increase in the rate of NO decomposition (18,19), ii) by Farr and Vayenas to electrochemically oxidize ammonia and cogenerate NO and electrical energy (20,21), iii) by Vayenas et al (11,12,22,23) to study the mechanism of several metal catalyzed oxidations under open circuit (potentiometric) conditions. 

Figure 3. Transient effect of electrochemical oxygen pumping. Conditions RC 2, Pi X 10-2 bar, P0jt = 9.5 X 10 2 bar, and 400°C.

The phenomenon appears to be due to formation and destruction of some type of surface silver oxide during oxygen pumping to and from the catalyst respectively. The use of in situ surface science techniques should prove very useful for the elucidation of the exact nature of this surface oxide. 

Several oxygen sensors based on oxygen pumping with stabilised zirconia have been reported (Hetrick, Fate and Vassell, 1981). This type of oxygen sensor is able to measure the oxygen partial pressure in the exhaust gas from the engine in lean burn. The operating principle of the... 

Figure 2 Schematic showing (a) potentiometric operation, (b) fuel cell operation and (c) electrochemical oxygen pumping.

Closed-circuit Behaviour - When a voltage is applied to such a cell there is a tendency for oxygen to migrate from one electrode to the other. As a result such arrangements have been used as oxygen pumps.18 20... 

Yttrium stabilized zirconia (Zr02-Y203) as an electrolyte for reduction of molecular oxygen at elevated temperatures (400-800°C) has been already discussed in Section 6.23.4. In fact, both the reduction of oxygen and the oxidation of the oxide ion at the Pt/zirconia interface is reversible and the transport of both species in zirconia is so rapid it is possible to construct an electrochemical oxygen pump, which is the heart of the limiting current oxygen sensor described in this chapter (Saji, 1987). The overall electrochemical reaction that takes place at the porous Pt electrode is... 

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