First-Principles Considerations on Catalytic Activity of Pd toward Ethanol Oxidation

The ethanol oxidation on Pd electrocatalysts is dramatically affected by the pH of the aqueous ethanol solution: no reaction occurs in acidic solutions, while the reaction is fast in alkaline solutions. A rationale for the origin of this pH effect on the ethanol oxidation to acetaldehyde has been provided by density functional theory (DFT) calculations. The DFT calculations show that in acidic media continued dehydrogenation of ethanol is difficult due to the lack of OH species to instantly remove hydrogen, which inhibits the ethanol electrooxidation. Conversely, both ethanol and sufficient OH can adsorb on Pd in alkaline media, leading to continuous ethanol electrooxidation.