Abstract. The electrochemical promotion of the ammonia decomposition reaction over Fe catalyst films interfaced with K2YZr(PO4)3, a K § and CaZr0.9In0.103. ~, a H § was investigated at temperatures 500-600 ~ At the higher temperatures, the catalytic rate was found to decrease significantly and reversibly upon decreasing the catalyst potential, VWR, i.e., upon pumping K § or H § to the Fe surface. The effect of potassium was more pronounced than that of protons leading to almost complete poisoning of the reaction. At the lower temperatures, it was found that electrochemical supply of moderate amounts of potassium causes an enhancement in the catalytic rate while higher amounts poison the reaction.The study reports, for the first time, electrochemical promotion over a Fe catalyst and shows that K § can also be used to induce the effect of Non-Faradaic Electrochemical Modification of Catalytic Activity (NEMCA). The effect of backspillover potassium ions and protons on the catalytic activity is discussed in terms of the theory of electrochemical promotion by considering the effect of varying catalyst work function on the coverages and chemisorptive bond strengths of NH 3, N and H. The results show the possibility of using electrically promoted catalyst pellets to alter the performance of industrial reactions. IntroductionThe use of solid electrolytes to induce the effect of nonfaradaic electrochemical modification of catalytic activity (NEMCA) or, electrochemical promotion (EP), or, in situ controlled promotion has been described for over 50 catalytic reactions during the last 9 years [1][2][3]. Work in this area has been reviewed recently [3]. The importance of the effect in electrochemistry, surface science and catalysis has been discussed by Bockris [4], Pritchard [5], and Haber [6], respectively.It has been found that the catalytic activity of metal electrodes interfaced with solid electrolytes can be markedly and reversibly affected by applying currents or potentials (typically +l-2V) between the catalyst film and a counter electrode also deposited on the solid electrolyte component. The increase in catalytic rate can exceed by a factor of 100 [3] or more [7] the open-circuit catalytic rate and can be up to a factor of 3-105 [3] higher then the rate of ion transport through the solid electrolyte.

It was found that the activity of Pt catalyst films interfaced with CeO, disks can be reversibly modified upon application of constant currents or potentials through the cell C2H4, 0,, C02, H,0, Pt CeO, Au, C,H4, O, C02, 1120 Negative current (or potential) application causes up to threefold enhancement in the rate of ethylene oxidation at temperatures 450-510°C. The rate increase is up to 3 >< 102 times higher than the rate, f/2F, of oxygen-ion transport through the mixed-conducting CeO2 support, if this was a pure ionic conductor. The observed nonfaradaic modification of catalytic activity is qualitatively very similar to that obtained when using pure anionic conductors, e.g., Y,02-stabilized-Zr02, and can be rationalized similarly, i.e., by considering the electrochemical induced changes in the work function of the catalyst and the concomitant changes of coverages and dipole moments of adsorbates. Apart from theoretical interest, the results are important in view of the current technological applications of ceria in automotive exhaust catalysts.

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