Paper SS+NS-ThA9
Geometrical, Electronic, and Vibrational Properties of Bare and H-covered Pt_n(n=22, 33, 44, 55, and 85) Nanoparticles

Thursday, November 1, 2012, 4:40 pm, Room 21

We have performed systematic density functional theory (DFT) calculations of the geometrical, electronic, and vibrational properties of small Pt_n nanoparticles (NPs) (n=22, 33, 44, 55, and 85) and their changes with NP size and adsorbate (H₂) coverage. We find our calculated H adsorption energy to be in range of –0.42 eV and -0.62 eV, and with increasing hydrogen coverage the H adsorption energy decreases due to adsorbate-adsorbate interactions. We find increase of Pt-Pt bond length upon hydrogen adsorption and, strikingly, the red shift of the center of the unoccupied d-bands of the bare Pt clusters turns to a blue shift upon hydrogen adsorption in good agreement with experiment [1]. We also find that there is a net charge transfer from all Pt atoms within the NPs to all hydrogen atoms of 0.55 (Pt₂₂H₂₂) and 1.37 electrons(Pt₄₄H₄₄). Thus, the remarkable hydrogen effect on the electronic structure of Pt NPs can be attributed to charge transfer from the Pt NPs to hydrogen. Regarding the optimal H coverage on Pt NPs, our calculated free-energy phase diagram shows non-zero H coverage even at beyond 600K under ambient H₂ pressure. This work is supported in part by US-DOE under Grant No. DE-FG02-07ER46354.

[1] F. Behafarid, L.K. Ono, S. Mostafa, J. R. Croy, G. Shafai, S. Hong, T. S. Rahman, Simon R. Bare, and B. Roldan Cuenya, submitted.