lonics 7 (2001) 237 Electrochemical Promotion of Pt During the Oxidation of Ethanol S. Douvartzides, K. Kyriakopoulos and P Tsiakaras* University of Thessalia, Department of Mechanical and Industrial Engineering, Pedion Areos, 383 34, Volos, Greece Abstract. The reaction of ethanol oxidation has been examined over a Pt polycrystalline film deposited on an yttria stabilized zirconia (YSZ) electrochemical reactor. Experiments were carried out at 325 ~ at atmospheric total pressure and under open and closed circuit conditions. It was found that the electrochemically-induced change in the catalytic rate of ethanol consumption is four orders of magnitude higher than the rate of ion transport through the solid electrolyte. The galvanostatic transient behavior of the consumption rates of ethanol and oxygen and of the formation rates of carbon dioxide and acetaldehyde have been also recorded. 1. Introduction During the last decades, the term Non-Faradaic Electro- chemical Modification of Catalytic Activity (or "electro- chemical promotion") has been adopted, in the very be- ginning from Vayenas and his school, and then also by others, as the most appropriate to describe those cases in which the catalytic performance of metals interfaced with solid electrolytes can be affected significantly upon external current or potential application. [1-5] Although electrochemical promotion has been the focal point of numerous studies aiming at the activation and control of various catalytic processes, the present work was undertaken to describe the unexamined reaction of ethanol oxidation over polycrystalline Pt deposited on yttria stabilized zirconia. In this respect, experiments were carried out initially in order to clarify the extend of the electrochemical promotion of Pt during ethanol oxidation. 2. Experimental The apparatus used in the course of the experiments has been described in detail in previous works [6,7]. The mixture of the reactant was formed by feeding streams of 21 vol.% 02 diluted in nitrogen and pure nitrogen (99.999 vol.%) in a saturator containing pure ethanol at 25 ~ and 1 bar. The adjustment of the feeding rates before the saturator was accomplished by using digital mass flow controllers (Brooks series 5800). The yttria stabilized zirconia (8 tool% Y2Os in ZrO2) atmospheric pressure, continuous flow well mixed (CSTR) reactor was a cylindrical tube closed flat at the bottom end with total volume 30 cm 3. On the inside bottom wall of the stabilized zirconia tube the porous Pt film was deposited by applying a thin coating of Engel- hard All21 Pt paste followd by drying and calcining in air first for 2 h at 450 ~ and then for 30 rain at 850 ~ The thickness of the Pt film was of the order of 5 p.m. The superficial surface area was 2 cruZ and the true surface area was of the order of 50 cm 2 as measured by a surface titration technique utilizing 02 and C2H 4. Then the number of the Platinum active centers was measured equal to Ypt ~ 4• -s g-atom Pt per gr of catalyst. Two similar Pt films were deposited on the outside bottom wall of the stabhilized zirconia which was ex- posed to ambient air and served as counter and reference electrodes, respectively. In the course of the experiments both galvanostatic and potentiostatic operation was used and both gave similar results. In the galvanostatic mode, a * Corresponding author. E-mail: tsiak@mie.uth.gr