Hydrogen Chemisorption on Pt80Fe20(111) Studied by TDS and UPS

Hydrogen adsorption on Pt80Fe20(111) has been investigated mainly by TDS and UPS. It has been compared to hydrogen adsorption on Pt(111) as the composition of the first layer of this alloy is almost pure platinum due to a strong surface segregation. It appears that the valence band of both clean surfaces is different and that the work function is lowered by 0.2 eV on the alloy compared to Pt(111). The work function changes induced by hydrogen adsorption are of the same sign and the same order of magnitude on both surfaces. Finally the activation energy for desorption of hydrogen is lower by about 2 kcal/mol on the alloy. Results are discussed in relation with the catalytic properties of this alloy in hydrogenation reactions.