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

The origin of electrochemical promotion was investigated via temperature-programmed desorption (TPD) of oxygen from polycrystalline Pt and Ag films deposited on YSZ under high-vacuum conditions and via measuring the work function of a Pt film deposited on YSZ under catalytic reaction conditions at atmospheric pressure. It was found that electrochemical O2− pumping to Pt and Ag catalysts in the presence of pre-adsorbed oxygen causes backspillover of large amounts of oxygen on the catalyst surface and leads to the formation of two oxygen adsorption states, i.e. strongly bonded anionic oxygen along 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. under electrochemical promotion conditions, a 1.42 eV increase in catalyst work function was observed. These results provide a straightforward explanation of the effect of electrochemical promotion on Pt and Ag deposited on O2− conducting solid electrolytes.