Outermost Surface Structures and Oxygen Reduction Reaction Activities of Co/Pt(111) Bimetallic Systems Fabricated Using Molecular Beam Epitaxy

Wadayama, Toshimasa; Yoshida, H.; Ogawa, Kazutoshi; Todoroki, Naoto; Yamada, Yoshiyuki; Miyamoto, K.; Iijima, Yuki; Sugawara, Tatsuya; Arihara, Kazuki; Sugawara, Seiho; Shinohara, Kazuhiko

doi:10.1021/jp203845u

Cited by 43 publications

(50 citation statements)

References 65 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Considering the CV and LSV results obtained in this study (Pt/Pd(111)), the shrinkage in Q H and a positive shift in the onset potential of hydroxyl species are common CV characteristics for highly active Pt-M(111) bimetallic surfaces. Because lattice mismatch between Pt and Pd is less than 1%, the much smaller changes in Q H and the positive shift in the hydroxyl species of Pt 1.2nm /Pd(111) relative to those of Ni or Co 26,29,31,32,50 might result from the relatively low compressive strains of the topmost Pt(111) lattice.…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Electrochemical Properties of Pt Epitaxial Layers Formed on Pd(111) in Ultra-High Vacuum

Bando

Takahashi

Todoroki

et al. 2015

J. Electrochem. Soc.

View full text Add to dashboard Cite

Electrocatalytic properties for oxygen reduction reaction (ORR) of Pt(111) epitaxial layers on a Pd(111) substrate are investigated. Scanning tunneling microscopy images of the as-prepared 0.6-nm-and 1.2-nm-thick Pt(111) epitaxial layers on Pd(111) (Pt 0.6nm /Pd(111) and Pt 1.2nm /Pd(111)) revealed that the topmost surface has atomically flat, 50-100-nm-wide terraces. Remarkable current features due to hydrogen storage and emission by the Pd(111) substrate dominated the cyclic voltammograms of Pt 0.6nm /Pd(111) in the potential range of 0.15-0.4 V vs. a reversible hydrogen electrode. In contrast, the curve of Pt 1.2nm /Pd(111) exhibited a shrinkage in the hydrogen charges (Q H ) in the potential range of 0.25-0.4 V, accompanied by the emergence of symmetrical redox features at 15 mV on the positive potential side, relative to Pt(111) "butterfly" feature. Both Pt 0.6nm /Pd(111) and Pt 1.2nm /Pd(111) showed ca. four times higher ORR activity than clean Pt(111), although their hydrogen-related behaviors and activity changes during applying potential cycles were much different. The results suggest that shrinkage in Q H and positive shift in the onset potential of hydroxyl species are common features of the CV of highly ORR-active well-defined Pt-M(111) bimetallic surfaces and that the activity enhancements and the structural stabilities fairly depend on the surface structure of the epitaxial Pt (111) High-performance low-cost polymer electrolyte membrane fuel cells (PEMFC) are required for wide-spread use in fuel cell vehicles. Developments in highly active oxygen reduction reaction (ORR) catalysts are one of the top priorities for developing PEMFC stacks. Since the pioneering work on Pt-M (M is a more affordable, lowcost material) alloys by Watanabe and co-workers, 1 numerous studies on the ORR properties of Pt-M bimetallic alloy with nanosized structures have been intensively performed. To date, several types of nanosized structures of Pt-M have been proposed for use as highperformance ORR catalysts, e.g., Pt-shell and M-core core-shell nanoparticles (NPs), 2-5 especially electrochemically de-alloyed M from Pt-M NPs, 6-9 nanostructured thin films of Pt-M, 10,11 shapecontrolled Pt-M NPs, [12][13][14][15] and nanoframe structures of Pt-Ni alloy. 16Irrespective of the proposed nature of the nanosized structures, the generation of electrochemically stable Pt-shell layers at the topmost surfaces is the consensus for synthesizing Pt-M ORR catalysts with high activity and durability. 17-20The topmost atomic-level structures of the Pt-shell layers for the Pt-M bimetallic alloys determine ORR performance. However, because ORR is governed by many factors, the discussions of ORR enhancement mechanisms are intricate. For example, atomic arrangements of the topmost Pt-shell, thickness of the Pt-shell layers, and interface structures between the surface Pt-shell and underlying M (Pt-M) core [21][22][23][24] are expected to have a serious influence on the ORR activities. When studying the topmost surface structures and the eval...

show abstract

Section: Resultsmentioning

confidence: 99%

“…z E-mail: n-todoroki@material.tohoku.ac.jp EC conditions were discussed for the Ni/Pt(111), [27][28][29][30][31] Co/Pt(hkl), 32,33 and Pt/Au(hkl) bimetallic surfaces. 34,35 In this study, we focused on the ORR activities of the Pt/Pd(111) bimetallic surfaces prepared through vacuum depositions of Pt on a Pd(111) substrate in UHV.…”

mentioning

confidence: 99%

Electrochemical Properties of Pt Epitaxial Layers Formed on Pd(111) in Ultra-High Vacuum

Bando

Takahashi

Todoroki

et al. 2015

J. Electrochem. Soc.

View full text Add to dashboard Cite

show abstract

“…One of the solutions for the improvement of ORR activity and the Pt utilization ratio is the use of Pt alloy catalysts. Many researchers have reported a higher ORR activity for binary and ternary alloys of Pt with 3d transition metals than for pure Pt [3][4][5][6][7][8][9][10][11][12][13][14][15]. Prior to the use of Pt alloy catalysts in PEFCs, because alloying elements dissolve from the catalyst and contaminate the proton exchange membrane [16], acid leaching treatment was commonplace [13,17].…”

Section: Introductionmentioning

confidence: 99%

Formation of Pt Skin Layer on Ordered and Disordered Pt-Co Alloys and Corrosion Resistance in Sulfuric Acid

et al. 2017

View full text Add to dashboard Cite

The formation of the Pt-enriched layer (Pt skin layer) formed at the surface of the ordered and disordered Pt-Co alloy specimens by a dealloying treatment and its corrosion resistance under potential cycling in sulfuric acid were examined to clarify the dissolution behavior of the Pt skin layer in polymer electrolyte fuel cell-operating conditions. The ordered and disordered Pt-Co specimens were obtained by heat treatment at 1073 and 1473 K, respectively. Co at the alloy surfaces dramatically dissolved in an early phase of the dealloying treatment in naturally aerated 0.5 M H 2 SO 4 at 298 K, and Pt skin layers were formed. Pt skin layers ca. 2 monolayer in thickness were formed on the Pt-Co alloy specimens by the dealloying treatment in 0.5 M H 2 SO 4 . The cyclic voltammetry measurements of the Pt-Co specimens showed the existence of Pt skin layers after the dealloying treatment and the inhibition of the Pt oxide formation on the Pt skin layers. The Pt oxide formation for ordered Pt-Co was more suppressed than that for the disordered Pt-Co. The Pt skin layers on the Pt-Co specimens exhibited a higher corrosion resistance than pure Pt, and the dissolution of the Pt skin layer for ordered Pt-Co was more inhibited than that for disordered Pt-Co under potential cycling in the potential range of 0.6-1.4 V in 0.5 M H 2 SO 4 (dissolution test). A thin, continuous Pt skin layer remained at the surface of the ordered Pt-Co specimen after the dissolution test. The formation of a uniform Pt skin layer seems to provide high oxidation resistance to the surface, leading to high corrosion resistance.

show abstract

“…10,1316) For example, Stamenkovic et al evaluated the ORR activities for the (111), (100) and (110) single crystal planes of a Pt 3 Ni intermetallic compound; their pioneering work clearly demonstrates that the (111) surface has a superior ORR activity. 13) Furthermore, molecular beam epitaxy (MBE) and ultra-high-vacuum (UHV) techniques enable the creation of well-defined bimetallic surfaces, and we have that the activities of the MBE-prepared Ni 0.3nm / Pt(111), 15) Co 0.3nm /Pt(111), (100), (110) 14,17) and Pt 0.3nm / Au(111) 18) bimetallic surfaces are very sensitive to the topmost and sub-surface structures. In either surface of the Pt-based well-defined single crystal alloys, the Pt-enriched topmost surfaces generated through thermal annealing in UHV reveal markedly high ORR activity.…”

Section: Introductionmentioning

confidence: 99%

Platinum-Enriched Ni/Pt(111) Surfaces Prepared by Molecular Beam Epitaxy: Oxygen Reduction Reaction Activity and Stability

et al. 2013

Self Cite

View full text Add to dashboard Cite

Oxygen reduction reaction (ORR) activities and electrochemical stabilities were evaluated for Ni/Pt(111) model electrode-catalysts fabricated by molecular beam epitaxy (MBE). Exposure of clean Pt(111) to 1.0-Langmuir (i.e., fractional coverage, ª = 1.0 in the Langmuir isotherm) CO at 300 K produced linear-bonded and bridge-bonded COPt IR bands at 2093 and 1858 cm ¹1. In contrast, 3.0-nm-thick Ni deposition onto Pt(111) at 823 K (823 K-Ni 3.0nm /Pt(111)) showed broad IR bands for adsorbed CO at around 2064 cm ¹1 ; the separation of reflection high-energy electron diffraction (RHEED) streaks of the 823 K-Ni 3.0nm /Pt(111) is greater than for clean Pt(111). In contrast, 923 KNi 3.0nm /Pt(111) yielded a single sharp IR band because of linear-bonded CO at 2080 cm ¹1, and the separation of the RHEED streaks is almost the same as that for the Pt(111). The results suggest that a Pt-enriched topmost surface is generated above 923 K through surface segregation of the substrate Pt atoms during the Ni deposition. After transferring the sample from ultra-high vacuum to an electrochemical system, without being exposed to air, changes in ORR activities of the MBE-prepared 923 K-Ni 3.0nm /Pt(111) were evaluated in a 0.1-mol L ¹1 HClO 4 aqueous solution under applied potential cycles of between 0.6 and 1.0 V vs. RHE. The ORR activity enhancement factor vs. clean Pt(111) for the asprepared 923 K-Ni 3.0nm /Pt(111) was estimated to be twelve, and this factor was reduced to four after the application of 1000 potential cycles. However, a 943 K-Ni 3.0nm /Pt(111) sample, which showed a relatively low ORR activity (an enhancement factor of eight), had the activity enhancement factor of six even after the application of 1000 potential cycles. These results reveal that the sub-surface structures and composition of Pt-based alloys determine not only initial ORR activity but also electrochemical durability of the ORR catalysts.

show abstract

Outermost Surface Structures and Oxygen Reduction Reaction Activities of Co/Pt(111) Bimetallic Systems Fabricated Using Molecular Beam Epitaxy

Cited by 43 publications

References 65 publications

Electrochemical Properties of Pt Epitaxial Layers Formed on Pd(111) in Ultra-High Vacuum

Electrochemical Properties of Pt Epitaxial Layers Formed on Pd(111) in Ultra-High Vacuum

Formation of Pt Skin Layer on Ordered and Disordered Pt-Co Alloys and Corrosion Resistance in Sulfuric Acid

Platinum-Enriched Ni/Pt(111) Surfaces Prepared by Molecular Beam Epitaxy: Oxygen Reduction Reaction Activity and Stability

Contact Info

Product

Resources

About