Adsorption behaviors of monomer and dimer of formic acid on Pt(111) in the absence and presence of water.

By performing density functional theory (DFT) theory calculations, we studied the adsorption behaviors of the monomer and dimer of formic acid (HCOOH, FA) on the Pt(111) surface with and without the presence of water molecules. The monomer prefers to stand on the surface of Pt(111), and in the most stable adsorption configuration the carbonyl O of HCOOH binds to the atop site of a Pt atom and the hydroxyl H points asymmetrically to two neighboring Pt atoms. The dimer of HCOOH not only exists in the gas-phase but also on Pt(111) surface, and the eight-membered ring dimer is identified as the energetically most favorable dimeric structure of HCOOH both in gas-phase and on Pt(111) surface. With the presence of water molecules, both the monomer and dimer of HCOOH prefer to lie parallel to the surface so as to maximize the number of H-bonds to adjacent water molecules. These results indicate that water molecules significantly influence the initial adsorption manner of HCOOH and further its decomposition reactivity on Pt(111) surface. The present work shows the adsorption behavior of HCOOH dimer on Pt(111) for the first time and also gives several new adsorption configurations of the monomer that are not reported in literature. The theoretical results are expected to provide a valuable input to understand the reactivity of HCOOH on Pt(111).