ORIGIN OF NON-FARADAIC ELECTROCHEMICAL MODIFICATION OF CATALYTIC ACTIVITY

X-ray photoelectron spectroscopy (XPS) was used to investigate the eff ect of electrochemical oxygen pumping on Pt catalyst films interfaced with an O2--conducting yttria-stabilized zirconia solid electrolyte. I t was found that electrochemical oxygen pumping to the catalyst causes spillover of significant amounts of anionic oxygen from the solid ele ctrolyte onto the platinum film surface. The spillover oxygen species has an XPS binding energy 528.8 eV compared to 530.4 eV for chemisorbe d 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 pump ing confirms the previously proposed explanation of the non-Faradaic e lectrochemical modification of catalytic activity (NEMCA) or electroch emical promotion in catalysis.