Do Ngoc Son

Proton transport through aqueous Nafion membrane

We introduce a new model for proton transport through a single proton-conducting channel of an aqueous Nafion membrane based on a mechanism in which protons move under electrostatic effect provided by the sulfonate ( SO3-groups of the Nafion side chains, the spin effect of active components, the hydrogen bonding effect with water molecules, and the screening effect of water media. This model can describe the proton transport within various levels of humidification ranging from the low humidity to the high humidity as a function of operating temperature. At low humidity, this model approaches to the so-called surface mechanism, while at high humidity, it approaches the well-known Grotthuss one. Proton motion is considered as the transfer from cluster to cluster under a potential energy. A proton-proton interaction is comprised in the calculation. Using Green function method, we obtained the proton current as a function of the Nafion membrane temperature. We found that the lower the temperature, the higher the proton current transfer through the Nafion membrane in low temperatures compared to the critical point 10K, which separates magnetic regime from non-magnetic regime. The increasing of proton current at very low temperatures is attributed to the spin effect. As the membrane temperature is higher than 40 °C , the decreasing of proton current is attributed to the loss of water uptake and the polymer contraction. The results of this study are qualitatively in good agreement with experiments. The expression for the critical temperature is also presented as a function of structural and tunable parameters, and interpreted by experimental data.

Oxygen Reduction on Pt(111) Cathode of Fuel Cells

We investigate the oxygen reduction reaction (ORR) on Pt(111) surface in the presence of hydronium ion. The ORR is proposed to proceed through two adsorption pathways: one is through the dissociative adsorption that forms adsorbed oxygen atoms O ad on the surface (“ad” means in the adsorbed state on the surface), followed by a reductive transition in the presence of hydronium ion that transits O ad into the adsorbed hydroxyl (OH) ad . In this pathway, the first electron transfers after dissociation of O 2 ; the other is through the molecular adsorption on the surface, followed by a reductive adsorption in the presence of hydronium ion in which first electron transfers after the O 2 adsorption to form the adsorbed end-on intermediate O ad OH before continuing the reaction with another hydronium ion to form the adsorbed hydroxyl (OH) ad . In both cases, the reaction is completed by the reductive desorption of (OH) ad in the presence of hydronium ion to form water molecules. In this work, we focus our study ...