Investigation of electrochemical promotion using temperature-programmed desorption and work function measurements

The origin of electrochemical promotion was investigated via temperature-pr ogrammed desorption (TPD) of oxygen from polycrystalline Pt and Ag films de posited on YSZ under high-vacuum conditions and via measuring the work func tion of a Pt film deposited on YSZ under catalytic reaction conditions at a tmospheric pressure. It was found that electrochemical O2- pumping to Pt an d Ag catalysts in the presence of pre-adsorbed oxygen causes backspillover of large amounts of oxygen on the catalyst surface and lends to the formati on of two oxygen adsorption states, i.e. strongly bonded anionic oxygen alo ng with weakly bound atomic oxygen. Furthermore, the desorption activation energy of oxygen adsorbed on Pt and Ag catalyst films was found to decrease linearly with increasing catalyst potential. Finally, by increasing the Pt -catalyst potential from -0.9 to +1.3 V during C2H4 oxidation on Pt, i.e. u nder electrochemical promotion conditions, a 1.42 eV increase in catalyst w ork function was observed. These results provide a straightforward explanat ion of the effect of electrochemical promotion on Pt and Ag deposited on O2 - conducting solid electrolytes. (C) 2000 Elsevier Science B.V. All rights reserved.