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