Composition Effect of Bimetallic PtAu Clusters on

the Adsorbed CO Vibrational Frequencies

Lichang Wang, Mark Sadek, Chunrong Song, Qingfeng GeChemistryChemistry && BiochemistryBiochemistry

Hydrogen Fuel Cell

2H2(g)4H+(aq) +4e-

O2(g)+4H+(aq) +4e 2H2O(g)

Challenge: Cathode catalysts

Cathode catalysts

• Pt

• PtRu

• PtFe

• PtAu

• PtVFe

PtAu nanoparticles• Shown to be the potential fuel cell catalyst • Nano-sized particles have superior catalytic properties over the larger particles• Exhibit different catalytic activities via different synthetic routes• Most experimental and theoretical studies focused on the surfaces of the bulk alloys

An insight into the underlying catalytic mechanismof PtAu nanoparticles is necessary

Research Goals

• Study PtAu nanoparticles total up to 55 metal atoms (~1.5nm)• Examine the interaction of CO with selected nanoparticles • Compare with CO adsorption on the surface of bulk alloy • Investigate CO vibrational frequency shift at different compositions

Computational Details—DFT in VASP

• Exchange & correlation: PW91

• Ion-electron interaction: PAW

• Basis set: Plane wave (400 eV cutoff)

• Distance b/w imagines: > 20 Å

Energy convergence: 0.05 eV/atom Frequency convergence: 10 cm-1

CO on PtAu dimers

Ads. energy (eV)

C—O (cm-1) M—CO (cm-1)

1.73 2091 434

1.81 2062 442

2.78 2021 522

2.25 2017 504

Free C—O frequency is 2134 cm-1

AuPtCO

CO on PtAu tetramers

Ads. energy (eV)

C—O (cm-1) M—CO (cm-1)

1.74 2081 447

1.87 2078 451

1.41 2051 430

2.89 2031 542

Free C—O frequency is 2134 cm-1

AuPtCO

CO on PtAu tetramers

Ads. energy (eV)

C—O (cm-1) M—CO (cm-1)

2.81 2017 531

1.53 2046 442

2.87 2023 532

2.70 2019 522

Free C—O frequency is 2134 cm-1

AuPtCO

CO on PtAu tetramers

Ads. energy (eV)

C—O (cm-1) M—CO (cm-1)

1.73 2091 434

1.81 2062 442

2.78 2021 522

2.25 2017 504

Free C—O frequency is 2134 cm-1

AuPtCO

Comput. Mater. Sci. 35 (2006) 247.

AuPtCO

$$$: MTC at SIUC

Conclusions

• CO frequency is less sensitive to the composition of a PtAu cluster

• CO frequency is less sensitive to the size of PtAu cluster

• CO frequency can be used to determine adsorption site