Typical Electrochemical Promotion Experiment

The combustion of ethylene occurs at the gas-exposed catalyst surface with a reaction rate, fo, expressed in terms of moles of atomic oxygen consumed per unit time (mol O s ). 

Application of an anodic current between the counter and the working electrode —now the solid electrolyte is the source of O ions and the working electrode is the collector of electrons— may result in the electrochemical oxidation of ethylene at the working electrode  

Assuming a current efficiency of 100%, the maximum possible electrochemical reaction rate, rparad (ntol 0 s ), is obtained from Faraday s law  

The electrochemical promotion is usually quantified by three parameters. A, p, and y. The enhancement factor, A, which may be 

For enhancement factors higher than nnity the reaction is called non-Faradaic. The rate enhancement factor, p, is defined as the ratio of the promoted catalytic rate, r, to the initial open-circnit reaction rate, r, and it is a measnre of the level of promotion  

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A typical electrochemical promotion experiment utilizing (3"-Al203, a Na+ conductor, as the promoter donor is shown in Fig. 4.15. The reaction under study is the oxidation of CO on Pt.51... 

A typical electrochemical promotion experiment includes kinetic measurements under open and closed circuit conditions as well as study of the effect of catalyst potential or work function on catalytic rate and selectivity under steady state and transient conditions. In kinetic measurements one should change the partial pressure of each reactant while... 

In order to estimate T P in actual electrochemical promotion experiments we use here typical values23 of the operating parameters (Table 11.2) to calculate J and galvanostatic transients which show that the lifetime of the promoting O5 species on the catalyst surface is typically 102 s at temperatures 350°-400°C. 

A typical apparatus for electrochemical promotion experiments consists of three parts (a) The gas feed and mixing system (b) the reactor and (c) the analysis and electrochemical measurements system. A detailed schematic of the experimental apparatus is shown in Figure B.l, where the three parts are clearly shown. 

Two types of continuous flow solid oxide cell reactors are typically used in electrochemical promotion experiments. The single chamber reactor depicted in Fig. B.l is made of a quartz tube closed at one end. The open end of the tube is mounted on a stainless steel cap, which has provisions for the introduction of reactants and removal of products as well as for the insertion of a thermocouple and connecting wires to the electrodes of the cell. A solid electrolyte disk, with three porous electrodes deposited on it, is appropriately clamped inside the reactor. Au wires are normally used to connect the catalyst-working electrode as well as the two Au auxiliary electrodes with the external circuit. These wires are mechanically pressed onto the corresponding electrodes, using an appropriate ceramic holder. A thermocouple, inserted in a closed-end quartz tube is used to measure the temperature of the solid electrolyte pellet. 

In order to estimate t]p in actual electrochemical promotion experiments we use here typical values [138] of the operating parameters (Table 4) to calculate J and The... 

It may be concluded that the use of a continuous, porous gold film as reference electrode in the given solid oxide electrochemical cell is an appropriate choice. It was shown to be catalytically inert and to have a reasonably stable potential. The estimated error of the latter is less than 20 mV under typical conditions of electro-chemical promotion experiments. The potential distribution in the solid electrolyte was shown to be highly sensitive to the exact position of the electrodes. Nevertheless, estimation of the catalyst potential remains reliable because the ohmic drop correction is almost negligible, e.g., at 375°C it is in the order of 1 mV pA . ... 

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