Non-faradaic electrochemical modification of catalytic activity (NEMCA) of propane oxidation on Pt/YSZ thin film cell

Abstract

In this work, non-Faradaic Electrochemical Modification of Catalytic Activity (NEMCA) of propane oxidation over Pt/yttria-stabilized zirconia (YSZ) thin films on alumina substrates has been studied. YSZ thin films were initially prepared by slurry dip coating and calcined at a relatively lower temperature of 800�oC. Propane oxidation at temperatures in a range of 300-500�oC clearly exhibited NEMCA. The maximum rate enhancement ratio was close to 3 at an applied potential of 1.0 V and a reaction temperature of 400�oC. The maximum faradaic efficiency was higher than 10,000 at an applied potential of 0.2 V and 300oC. However, NEMCA was not observed at 200 ?C. Nevertheless, the reproducibility of this cell was poor mainly because of weak adhesion between the YSZ film and the alumina substrate. This was caused by the low calcination temperature for the YSZ film. A higher temperature could not be used because the gold counter electrode had been found to diffuse into the alumina substrate at higher temperatures and lost its conductivity. For this reason, fabricated YSZ thin films adhered only weakly to alumina substrates and had a low-conductivity, highly porous structure. Copper doped bismuth vanadate (BICUVOX.10), which is a sintering aid, was added to the recipe for YSZ thin films to lower the films' sintering temperature. The BICUVOX.10 powder was prepared and characterized with XRD, XPS and DSC. The obtained XRD diffractogram and DSC curve confirmed the existence of a new phase transition. Composite films of YSZ and BICUVOX.10 were fabricated by screen printing and calcination 800 ?C. XRD analysis showed no solid-state reaction between YSZ and BICUVOX.10. Surface micrographs of thin film showed that increasing the BICUVOX.10 concentration resulted in a denser structure of the composite films. However, the addition of BICUVOX.10 decreased the open-circuit reaction rate due to the reduced surface areas of thin films. Nevertheless, increasing the concentration of BICUVOX.10 in thin films resulted in higher sensitivity of the reaction rate to the applied potential under anodic polarization region. The highest faradaic efficiency was obtained at 2.5 % BICUVOX.10.