The effect of catalyst-electrode potential and work function on the chemisorptive bond of oxygen on Pt interfaced with YSZ

Controlled variation in catalyst-electrode potential of metals interfaced with solid electrolytes leads to the effect of Non-faradaic Modification of Catalytic Activity (NEMCA) which causes dramatic changes in the catalytic activity and selectivity. Its origin was shown to lie in the controlled variation of the work function upon polarization of the catalyst-solid electrolyte interface which is due to ion spillover over the entire gas exposed catalyst surface. In the present work the effect of induced work function changes on the kinetics and energetics of the interaction of oxygen with polycrystalline Pt, interfaced with an yttria stabilized zirconia solid electrolyte, were studied, by means of the temperature programmed desorption technique. It was found that by increasing catalyst potential and work function the O₂ desorption peak shifts towards lower temperatures, showing that the binding strength of chemisorbed oxygen species weakens by increasing catalyst work function. The activation energy of desorption of adsorbed O species was measured by the “temperature rate variation technique” and was found to decrease linearly with slope -1 with increasing catalyst work function. This straightforward experimental correlation between catalyst work function and the binding energy of chemisorbed O species is in absolute agreement with previous NEMCA studies which show that the apparent activation energy of all reactions studied, depends linearly on catalyst potential and work function. Paper presented at the 1st Euroconference on Solid State Ionics, Zakynthos, Greece, 11 – 18 Spt. 1994