| With the predicted limitations of the fossil reserves around the world and the growing pollution related to their consumption, it is in the human being's interest that we find some alternative less polluting energy resources or vectors for our needs. A promising road leads us to the usage of fuel cells. Efforts have been made to improve the already promising DMFC (direct methanol fuel cell). Methanol being too toxic to humans, studies, including those developed recently in our group, have contributed in the increase in the performances of Direct Acetal Fuel Cells (DAFC) This work follows previous works of Narayanan, Savadogo, and more closely, Yanick Cyr's Master Thesis. For the first time, the present research focuses on determining the effect of acetal's cross-over on the DAFC cathode behavior. It is widely demonstrated that the liquid fuels like alcohols or acetals cross over to the cathode by permeation through the electrolyte membrane. Until now the fuel cross-over problem was expected, in general, to be minimized through an appropriate choice of the polymer electrolyte membrane. In this work we will show that one other elegant approach consists in looking for acetals tolerant cathode for the Oxygen Reduction Reaction (ORR).; All tests were conducted in an electrochemical cell in order to simulate the working conditions of an acetal fuel cell. Several different catalysts (Pt, Pt/C, PtRu/C, PtSn/C, and PtIr/C) where used to see their behavior in the instance of fuel crossover. The fuels used in this study were methylal, ethylal, 1,3-dioxolane, and for comparison, methanol. The latter will serve as a referral since acetals are not well documented. Cyclic voltammograms and potentiostatic tests helped to determine the electrochemical properties and reaction kinetics of the fuels. Furthermore, the use of HPLC (high performance liquid chromatograph) and the mass spectrometer, a semi-quantitative analysis of the products was made over a period of 10 000 seconds.; It was observed that the oxidation of the fuels (0,5M) on pure platinum electrode hindered greatly the process of the oxygen reduction. When adding methylal in presence of oxygen, the oxygen reduction. When adding methylal in presence of oxygen, the oxygen reduction (ORR) onset potential would drop from 1,000V/RHE to 0,41V. Using ethylal, 1,3-dioxolane and methanol, we come to the same conclusions since we obtain ORR potentials of 0,47V, 0,44V and 0,77V respectively for each fuel.; In conclusion, we observe that among all catalysts used, the Pt/C based electro-catalyst is the cathode which exhibited the smallest onset potential. In a similar way, it was shown that the lowest onset potentials were obtained when PtIr/C catalyst was used as electro-catalyst for ethylal and 1,3-dioxolane fuels. The onset potential of methanol contacting the electro-catalyst cathode is higher on Pt/C than all the other binary electro-catalyst, indicating that the ORR might be less affected by the presence of this fuel in the case of Pt/C.; At the end of the document we listed the recommendations which will help to improve the development of direct acetal fuel cells. (Abstract shortened by UMI.)... |
