With direct alcohol fuel cells (DAFC) the chemical energy of the reactants can be directly converted to electrical energy that can be used for instance in portable applications, independent of the electrical network. Liquid fuels such as organic alcohols are interesting for customer applications because they are more facile to use and relatively safe when compared with gaseous hydrogen. However, the obstacles to commercialization are the expensive cell components, catalysts and electrolyte membrane, as well as the limited lifetime of current systems due material decomposition. In order to make this technology commercially viable new cost effective and more durable materials must be introduced and this thesis highlights the ex situ and in situ methods for studying these materials in DAFC related conditions. The first part introduces methods to detect anode reaction products ex situ. The results indicate that at DAFC anode related potentials formic acid, formaldehyde and carbon dioxide are detected for methanol, acetaldehyde and acetic acid for ethanol and only acetone for isopropanol. In addition, HPLC analyses revealed that in alkaline media Pt based catalyst would be more preferable than Pd for methanol and ethanol oxidation, however, for isopropanol oxidation Pd shows increased performance. Moreover, the surface structure sensitivity of these reactions is studied with Pt single crystal electrodes and results imply that a strong effect on onset potential and activity exists: the Pt(111) surface being the most active for isopropanol and Pt(100) for methanol and ethanol oxidation. The second part discusses the properties, preparation and performance of nanoparticle catalyst. A Pd catalyst prepared with ALD method showed increased activity for ethanol and isopropanol oxidation due to the evenly distributed catalyst on the carbon support. Moreover, the effect of various nanocarbon supports was studied and they showed high activity and durability in ex situ experiments, however, this activity was lost in the in situ tests implying that the MEA preparation needs to be optimized individually as each support material possesses different polarities. The third part introduces proton and anion exchange membrane DAFCs and shows the effect of catalyst, carbon support, anode fuel and the membrane material to the cell performance and durability. It can be concluded that in DAFCs exist also various phenomena that cannot be observed with solely ex situ techniques. The results reported in this thesis are relevant to the fundamental understanding of the DAFC phenomena occurring on the electrodes and in the MEA and highlight the importance of both ex situ and in situ experiments.
|Translated title of the contribution||Suora-alkoholipolttokennojen anodimateriaalien tutkiminen|
|Publication status||Published - 2012|
|MoE publication type||G5 Doctoral dissertation (article)|
- alcohol oxidation