Formic Acid Oxidation at Pt/H2O Interface from Periodic DFT Calculations Integrated with a Continuum Solvation Model

As an important class of catalytic reactions, the reaction at solid/liquid interfaces is less understood at the atomic level. From a theoretical point of view. the difficulty lies at the simultaneous consideration of the extended solid surface and the dynamic liquid environment. In taking the oxidation of formic acid (HCOOH -> CO2 + H-2) at the Pt(111)/H2O interface as the model system that has great potentials in direct fuel Cells applications, this work combines density functional theory (DFT) slab calculations with a Continuum solvation model to simulate the reactions at the metal/H2O interface for the first time. The solvation effect is treated by including (i) a few explicit. water molecules as the core solvation shell and (ii) an implicit continuum solvation model to take into account the long-range electrostatic interaction from water solution. We show that formic acid can be directly oxidized to CO2 only in the presence of preadsorbed formate. Although the formate itself can not be oxidized to CO2 at mild conditions, it helps to stabilize the formic acid adsorption configuration with the CH bond in contact with the Pt surface. which is the precursor leading to CO2. Without the preadsorbed formate. formic acid is only able to adsorb with its carboxyl O linking to Pt, which is however difficult to decompose further. By electronic structure analyses, we show that a hydrophobic zone formed nearby the preadsorbed formate on Pt(111) is the origin for the promoting role of formate, which demonstrates that catalytic reactions at solid/water interface can be significantly affected by modifying the affinity between Surface and water.