A DFT Study of Hydrogen Adsorption on Metallic Platinum: Associative or Dissociative Adsorption

In this study, the molecular and atomic adsorption energies, and total density of states (DOS) of the hydrogen on the on-top, bridge, and hollow positions of FCC (100), and FCC (111) surfaces of the metallic platinum were investigated using the DFT calculations. The total DOS result shows higher interaction between hydrogen molecule and metallic surface for the FCC (111) than the FCC (100) surface. Also, the intensity of the anti-bonding orbital for the bridge position is higher than two other positions on the FCC (100) surface, which shows that the hydrogen molecule in this position is ready to be dissociated into hydrogen atoms. In addition, the intensity of the anti-bonding orbital for hollow and bridge positions are higher than the on-top position on FCC (111) surface, which shows the hydrogen molecule in these positions are dissociated into hydrogen atoms. The results show that the comparison between the activation barrier energy (ΔEads) calculated from Lennard-Jones potential curves, and molecular adsorption energy determines whether the hydrogen molecule is dissociated on the surface. If the activation barrier energy (ΔEads) is higher than molecular adsorption energy, the probability that the hydrogen molecule will dissociate on the surface is very low.