ORIGIN OF NON-FARADAIC ELECTROCHEMICAL MODIFICATION OF CATALYTIC ACTIVITY

X-ray photoelectron spectroscopy (XPS) was used to investigate the effect of electrochemical oxygen pumping on Pt catalyst films interfaced with an O2--conducting yttria-stabilized zirconia solid electrolyte. It was found that electrochemical oxygen pumping to the catalyst causes spillover of significant amounts of anionic oxygen from the solid electrolyte onto the platinum film surface. The spillover oxygen species has an XPS binding energy 528.8 eV compared to 530.4 eV for chemisorbed oxygen, which is also observed on the surface, and is less reactive than chemisorbed oxygen with the reducing ultrahigh vacuum background. The detection of the anionic oxygen species upon electrochemical pumping confirms the previously proposed explanation of the non-Faradaic electrochemical modification of catalytic activity (NEMCA) or electrochemical promotion in catalysis.