Permanent electrochemical promotion of C3H8 oxidation over Pt thin films

S. SOUENTIE; L. LIZARRAGA; E.I. PAPAIOANNOU; C.G. VAYENAS; P. VERNOUX

Las Vegas

Encuentro; 218th Electrochemical Society Meeting; 2010

The Electrochemical Society

Electrochemical promotion of catalysis (EPOC or NEMCA effect) has been investigated thoroughly for more than 70 catalytic reactions [1,2]. In electrochemical promotion studies the conductive catalyst-electrode is in contact with an ionic conductor and the catalyst is electrochemically promoted by applying a current or potential between the catalyst film and a counter or reference electrode, respectively [1,2]. Numerous surface science and electrochemical techniques [1-3] have shown that EPOC is due to electrochemically controlled migration of promoting or poisoning ionic species (O2- in case of YSZ) between the ionic or mixed ionic-electronic conductor and the gas exposed catalytic surface. In EPOC studies, after current interruption the catalyst restores its initial activity within few minutes indicating the reversibility of the phenomenon. However, recent studies [3,4] have demonstrated a “permanent” effect of the anodic polarization on the catalytic rate for a long time period after current interruption which strongly depends on the polarization time (2-8 hours). This effect has been described as “permanent electrochemical promotion of catalysis” (PEPOC) [4]. Recent studies have shown that P-EPOC possibly originates from the oxygen species storage occurring at the Pt/YSZ interface upon anodic polarization [3,4]. After current interruption these oxygen species migrate to the three phase boundaries (TPBs) and spread out over the gas-exposed catalyst surface acting as promoters for the catalytic reaction [4]. However, after total consumption of the stored oxygen species, the catalyst restores its initial activity [3,4].