1P112
First-Principle Study of Pt55 and Core-Shell Ru13@Pt42 Catalysts forOxygen Reduction Reaction
1○ Jing Lu1, Kazuya Ishimura2, and Shigeyoshi Sakaki*1
Fukui Institute for Fundamental Chemistry (FIFC), Kyoto University,
Takano-Nishihiraki-cho 34-4, Sakyou-ku, Kyoto 606-8103, Japan
2
Institute for Molecular Science (IMS), Okazaki 444-8585, Japan[Abstract] First-principle calculations were performed to investigate the preferential site on
the Pt42 surface of icosahedron-like Ru13@Pt42 and Pt55 for interaction with O2, OOH, O, andOH. Ru13@Pt42 has weaker binding ability for O2 than Pt55. The O-OH bond cleavage ofOOH-containing species occurs with small barrier for Pt55 and Ru13@Pt42. Both of OH(OHPt)
and OHHPt formation reactions participate in rate-determining process in Ru13@Pt42 catalyst.
On the other hand, OH(OHHPt) formation reaction is rate-determining step (RDS) in Pt55
catalyst. The barrier of RDS in the case of Ru13@Pt42 is smaller than that of Pt55, suggestingthat Ru13@Pt42 could serve as a promising ORR heterogeneous catalyst like Pt55.
[Introduction] Pt-based clusters/particles are one of efficient catalysts for oxygen reduction
reaction (ORR) at the cathode in proton exchange membrane fuel cells (PEMFCs) because of
their incomparable catalytic activity. However, the limited resource and high cost of Pt, as
well as the slow reaction of ORR, have remained as the major hurdles for commercializationof PEMFCs. Pt alloys with core-shell structure (M@Pt) have been shown great promise as
next generation ORR catalysts due to their superior catalytic performance and lower cost thanpure Pt. M@Pt catalyst can significantly improve the Pt utilization by depositing a thin Pt
shell outside the M core. The structural and electronic effects of M element in the core play
crucial roles in weakening the ability to bind with oxygen species. In general, an ideal catalyst
should exhibit a moderate interaction between Pt surface and oxygen species. O2 activationand electron transfer will be hampered if theability to bind with oxygen-containing
adsorbates is too weak. Conversely, if suchbinding ability is too strong, the subsequent H2O
formation will be sluggish.
Previously, the stability of icosahedron-like
Pt42Ru13 cluster were investigated in our group.
The core-shell structure (Ru13@Pt42) is much
more stable than these non-core-shell structures(PtRu12@Pt41Ruedge and PtRu12@Pt41Ruvert.).
However, further theoretical insights into thecatalytic performance of Ru13@Pt42 and Pt55
catalysts toward ORR is limited and highlydesirable. Our purposes are to elucidate theORR mechanism and rate-determining step(RDS) in Ru13@Pt42 and Pt55 catalysts.
[Methods] All the spin-polarized calculations
were performed with the Vienna Ab initio
Simulation Package (VASP). The PBE-D3
method was adopted for geometry optimization

Scheme 1. (a) Binding sites on the surface of
icosahedron-like Pt42. (b) Schematic illustrationof reaction pathways for ORR.

with an energy cutoff of 400 eV. The cluster was placed in a sufficiently large supercell (25 Å× 25 Å × 25 Å) to ensure enough separation by vacuum. The thresholds for energy and force
were set at 0.0001 eV and 0.01 eV/Å, respectively. The reaction energy barrier was calculatedusing Nudged Elastic Band (NEB) method with VASP Transition State Tools (VTST). To
estimate the solvent effect, an implicit solvation model, which describes the effect ofelectrostatic interaction between solute and, was used in VASP.
[Results and Discussion] The adsorption sites on the Pt42 surface of icosahedron-like
55-atom clusters are shown in Scheme 1a. The preferential sites for O2, OOH, and O-bindingon the Pt42 surface of Ru13@Pt42 and Pt55 are b1, t2, and h1, respectively. For OH-binding, theb1 and t2 sites are preferable in Pt55, while only t2 is the most favorable in Ru13@Pt42.
Ru13@Pt42 has a weaker ability than Pt55 to bind with O2, OH, and so on. It can be reasonably
explained via lower energy shift of d-band center for Ru13@Pt42 due to compressive strain
effect of Pt42 surface and charge transfer from Pt42 shell to Ru13 core. The calculated d-band
center for Ru13@Pt42 is -2.18 eV, which is lower than that for Pt55 (-2.02 eV).
The full catalytic cycle of ORR is descripted in Scheme 1b. For both catalysts, the O-OH
bond cleavage occurs with small barrier. For Ru13@Pt42, the OH(OHPt), OH(OHHPt), andOHHPt formations need barriers of 0.86 eV, 0.76 eV, and 0.89 eV, respectively. For Pt55, theOH(OHPt), OH(OHHPt), and OHHPt formations need barriers of 0.57 eV, 1.10 eV, and 0.91 eV,respectively. Thus, OH(OHPt) and OHHPt formation reactions participate in rate-determining
process in Ru13@Pt42 catalyst. OH(OHHPt) formation reaction is the RDS in Pt55 catalyst. Thebarrier of RDS in the case of Ru13@Pt42 is smaller than that of Pt55.
Note that the direct H addition to O of oxygen containing species is also possible andmuch easier than H addition to Pt shell. The full catalytic cycle can be easily describedwithout HPt containing species 3, 6, 8, 11 (Scheme 1b). Our results verify that Ru13@Pt42
could serve as a less expensive ORR catalyst with desirable performance and a similar ORR
mechanism to Pt55 catalyst.

Fig. 1. Potential energy surfaces in the cases of Ru13@Pt42 in solution.

This work is based on results obtained from a project commissioned by the New Energyand Industrial Technology Development Organization (NEDO).
[References][1] M. E. Scofield et al. Chem. Soc. Rev. 44, 5836 (2015).
[2] J. Lu et al. J. Phys. Chem. C 122, 9081 (2018).