الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 173 |  |  |
| | | from | 173 | | |
Abstract
The aim of the present work is to study some electrocatalytic reactions related to Fuel cells such as methanol, ethanol oxidation and ORR. The oxidation of methanol proceed via the parallel pathway mechanism, one pathway “indirect” is through the formation of COad and then CO2, the other pathway “direct” is through the formation of dissolved intermediates such as HCHO and HCOOH and the formation of CO2 from such intermediates is negligible under convection conditions. The presence of Ru facilitates the adsorption and oxidation of methanol at Pt electrode.
Acetaldehyde is the main oxidation product for the oxidation of ethanol at polycrystalline platinum, Pt(11,1,1) and Sn modified Pt(11,1,1) with a current efficiency reaching to ca. 100 %. At Sn modified Pt(311), however, the onset of ethanol oxidation shifted by ca. 0.2 V to the negative direction comparing to bare Pt(311) with a huge increase of the oxidation current at low potential. Some potentiostatic measurements were done in this potential region to be sure whether this shift is accompanied by CO2 formation, i.e. C-C bond breaking, or not. In all cases, CO2 current efficiencies were zero and acetaldehyde current efficiencies were lower than 100 %, imply that acetic acid is also formed as an oxidation product.
The rate determining step during the oxidation of methanol and reduction of oxygen at polycrystalline platinum were assigned by using ac-Voltammetry technique and employing the idea of potential modulation. At such technique, the Tafel slope calculated from the normal method is comparing to that calculated from the apparent charge transfer coefficient (α’). The advantage of ac-Voltammetry technique comparing to normal method is that the Tafel slope in the apparent charge transfer coefficient is calculated is a very small potential range (just the ac amplitude) which minimize the small changes in the coverage during the sweep.