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

Abstract

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 → CO 2 + H 2 ) at the Pt(111)/H 2 O 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/H 2 O 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 CO 2 only in the presence of preadsorbed formate. Although the formate itself can not be oxidized to CO 2 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 CO 2 . 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 fomate 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.