Electrochemical Behavior of Supported Pd Electrocatalysts with High Activity and Selectivity towards the ORR in Ethanol-Containing Acid Solution

In this work, we studied the electrochemical behaviour of carbon-supported Pd electrocatalysts for the oxygen reduction reaction (ORR) in acid medium containing several concentrations of ethanol. For comparison, a Pt/C electrocatalyst was studied as well. The results indicate that this type of Pd-based cathode materials shows a remarkable selectivity toward the ORR and a high degree of tolerance to ethanol and/or intermediate species produced during the reaction. The tolerance and the activity for the ORR of Pd/C remains notable and worth considering even at higher concentrations of ethanol, i.e., the onset potential for the ORR and the ORR current densities on the palladium-based electrocatalysts are not significantly affected by the presence of C₂H₅OH molecules. This electrochemical behaviour differs from that of Pt/C, which is greatly affected by ethanol in terms of a displacement of the onset potential towards more negative potentials and lower ORR current densities. This displacement of the onset potential is obviously related to a higher cathodic overpotential of the Pt/C material in the presence of ethanol, compared to the overpotential of Pd/C electrocatalysts under the same experimental conditions. Even if the Pd/C electrocatalysts show a slightly lower activity for the ORR related to the activity of Pt/C in an alcohol-free sulphuric acid solution, the high performance demonstrated by the former in the ethanol-containing electrolytes indicates that this type of electrocatalysts or their alloys can find application in fuel cells fuelled with organic substances (e.g., ethanol, ethylene glycol or methanol). Thus, a better performance of a Direct Ethanol Fuel Cell can be expected if ethanol-tolerant cathode electrocatalysts such as Pd/C are used instead of Pt alone-based cathode materials. These results will contribute to the development of novel carbon-supported Pd-based electrocatalysts which possess a high activity for the ORR and a high degree of tolerance to organic fuels for application in Direct Fuel Cells.