Role of Water and Adsorbed Hydroxyls on Ethanol Electrochemistry on Pd: New Mechanism, Active Centers, and Energetics for Direct Ethanol Fuel Cell Running in Alkaline Medium

First principles calculations with molecular dynamics are utilized to simulate a simplified electrical double layer formed in the active electric potential region during the electrocatalytic oxidation of ethanol on Pd electrodes running in an alkaline electrolyte. Our simulations provide an atomic level insight into how ethanol oxidation occurs in fuel cells: New mechanisms in the presence of the simplified electrical double layer are found to be different from the traditional ones; through concerted-like dehydrogenation paths, both acetaldehyde and acetate are produced in such a way as to avoid a variety of intermediates, which is consistent with the experimental data obtained from in situ FTIR spectroscopy. Our work shows that adsorbed OH on the Pd electrode rather than Pd atoms is the active center for the reactions; the dissociation of the C-H bond is facilitated by the adsorption of an OH- anion on the surface, resulting in the formation of water. Our calculations demonstrate that water dissociation rather than H desorption is the main channel through which electrical current is generated on the Pd electrode. The effects of the inner Helmholtz layer and the outer Helmholtz layer are decoupled, with only the inner Helmholtz layer being found to have a significant impact on the mechanistics of the reaction. Our results provide atomic level insight into the significance of the simplified electrical double layer in electrocatalysis, which may be of general importance.