Electrochemical Promotion with Na-Conducting Solid Electrolytes

ELECTROCHEMICAL PROMOTION WITH Na -CONDUCTING SOLID ELECTROLYTES 

It has been shown that AI2O3, a Na conductor, can also induce 

NEMCA on metal surfaces. Here, the dominant electrocatalytic reaction is 

Ethylene oxidation on Pt/jS -AI2O3 was studied at temperatures between 150 and 300°C, but most of the NEMCA experiments were carried out at 290°C. Experimental details about the cell can be found in Ref. 42. The open-circuit kinetic behavior was found to be similar to the case of C2H4 oxidation on Pt/doped Z1O2 (Section IV. 1) that is, the rate expression 

As shown in Fig. 76, when the circuit is opened (/ = 0), the catalyst potential starts increasing but the reaction rate stays constant. This is different from the behavior observed with 0 -conducting solid electrolytes and is due to the fact that the spillover oxygen anions can react with the fuel (e.g., C2H4, CO), albeit at a slow rate, whereas Na(Pt) can be scavenged from the surface only by electrochemical means. Thus, as shown in Fig. 76, when the potentiostat is used to impose the initial catalyst potential, = -430 mV, then the catalytic rate is restored within 1(X)-150 s to its initial value, since Na(Pt) is now pumped electro-chemically as Na back into the j8 -Al203 lattice. 

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V. ELECTROCHEMICAL PROMOTION WITH Na" -CONDUCTING SOLID ELECTROLYTES... 

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