The Behavior Of The Overpotential And Underpotential Deposited Hydrogen on Pt(111) Electrodes: A Theoretical Study

PAOLA QUAINO; ELISABETH SANTOS; WOLFGANG SCHMICKLER

Nice

Congreso; The 61st Annual Meeting of the International Society of Electrochemistry. Electrochemistry from Biology to Physics; 2010

International Society of Electrochemistry - ISE

It is well known that the hydrogen electrode reaction (HER) is verified through thefollowing elementary steps, Tafel, Volmer and Heyrovsky. Therefore the reaction evolves through an adsorbed intermediate (Had) on an active site (s) on the metal electrode. A deep look into the bibliography corroborates the existence of two types ofadsorbed hydrogen on the metal surface. Underpotential deposited hydrogen (Hupd) and overpotential deposited hydrogen (Hopd). The latter would be the intermediate in the reaction. But for years, there have been many speculations about the location of theHupd and Hopd and their effect on the reaction. Several authors reported spectroscopic evidences trying to explain the similarities and differences of these twotypes of hydrogen. Although much effort was spent to elucidate the effect of theadsorbed intermediate, there is still a lack of knowledge and the behavior of these twotypes of hydrogen remains not well understood. Therefore, the purpose of our work is to investigate these two types of hydrogen adsorption (Hupd and Hopd) on Pt(111)-metal-surfaces in the framework of density functional theory to clarify their behavior and their contribution to the hydrogen electrode reaction. As our starting point, a series of calculations for the dissociation and adsorption of the H2 molecule for different coverages of Hupd have been done, and calculated the minimum energy, as well as the local density of states of the Hupd , the metal d band and the bonding and antibonding of the molecule. Our preliminary results show that the activation energy for the Tafel step decreases with decreasing the coverage of Hupd due to a steric effect and repulsive interaction between these hydrogens.