Oxygen Reduction Reaction Activity for Strain-Controlled Pt-Based Model Alloy Catalysts: Surface Strains and Direct Electronic Effects Induced by Alloying Elements

Masato Asano, Ryutaro Kawamura, Ren Sasakawa, Naoto Todoroki, Toshimasa Wadayama

Research output: Contribution to journalArticle

46 Citations (Scopus)

Abstract

Surface strain and electronic interactions (i.e., strain and ligand effects) play key roles in enhancing the oxygen reduction reaction (ORR) catalytic activity of Pt-based alloy catalysts. Herein, we evaluate the ORR activity enhancement factors for Pt(111)-shell layers on Pt25Ni75(111) single-crystal surfaces prepared by molecular beam epitaxy under ultrahigh vacuum (UHV). Scanning tunneling microscopy images of the pristine surfaces collected under UHV revealed periodic surface modulations, known as Moiré patterns, suggesting that the topmost Pt(111)-shell layers are compressively strained by the influence of the underlying Ni atoms. The correlation between the ORR activities and estimated strains for 3-ML- and 4-ML-thick Pt shells (where ML represents monolayer), each having -1.7% and -1.2% strained Pt-shells, correspond well to the strain-based theory predictions. On the other hand, a 2-ML-thick Pt shell, with -2.8% strain, exhibits a remarkable ORR activity enhancement, i.e., 25 times higher than the pristine Pt(111): the enhancement factor anomalously deviates from the value predicted by the strain-based theory. Therefore, the activity enhancement of the 2-ML-thick Pt sample can be ascribed to a ligand effect induced by the Ni atoms just below the topmost Pt(111)-shell layer. The results obtained in this study provide a fundamental insight into the ORR activity enhancement mechanisms of Pt-based electrocatalysts.

Original languageEnglish
Pages (from-to)5285-5289
Number of pages5
JournalACS Catalysis
Volume6
Issue number8
DOIs
Publication statusPublished - 2016 Aug 5

Keywords

  • oxygen reduction reaction
  • platinum-based alloy catalysts
  • polymer electrolyte fuel cell
  • scanning tunneling microscopy
  • strain and ligand effect

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)

Fingerprint Dive into the research topics of 'Oxygen Reduction Reaction Activity for Strain-Controlled Pt-Based Model Alloy Catalysts: Surface Strains and Direct Electronic Effects Induced by Alloying Elements'. Together they form a unique fingerprint.

  • Cite this