Surface segregation and stability of core–shell alloy catalysts for oxygen reduction in acid medium

Ramírez-Caballero, Gustavo E.; Ma, Yan; Callejas-Tovar, Rafael; Balbuena, Perla B.

doi:10.1039/b917899f

Cited by 119 publications

(89 citation statements)

References 69 publications

(84 reference statements)

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“…The surface segregation behavior is closely associated with the surface energy and atomic radius. 49,50 Because the atomic radii of the alloying elements (Cu, Ni and Co) are very similar, we believe that the surface energy should be more influential: 2.417 (Fe), 1.790 (Cu), 2.380 (Ni) and 2.522 (Co) J m − 2 . 51 Cu and Ni have lower surface energies than Fe, thus describing the easier surface segregations of Cu and Ni satisfactorily, whereas Co has a relatively higher surface energy (Figure 5d).…”

Section: Thickness Of Carbon Shells For Orr Activitymentioning

confidence: 99%

Towards a comprehensive understanding of FeCo coated with N-doped carbon as a stable bi-functional catalyst in acidic media

et al. 2016

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The identification and development of efficient catalysts made of non-precious materials for oxygen reduction reaction (ORR) are essential for the successful operation of a wide range of energy devices. This study provides evidence that earth-abundant nanoparticles of transition metals encapsulated in a nitrogen-doped carbon shell (M@N-C, M = Fe, Co, Ni, Cu or Fe alloys) are promising catalysts in acidic solutions. By density functional theory calculations and experimental validations, we quantitatively propose a method of tuning the ORR activity of M@N-C by controlling the nitrogen-doping level, the thickness of the N-C shells and binary alloying. FeCo@N-C/KB was chosen as the best ORR catalyst because of its onset and half-wave potentials of 0.92 and 0.74 V vs a reversible hydrogen electrode (RHE), respectively, and its excellent durability. Furthermore, FeCo@N-C/KB possesses a high activity for the hydrogen evolution reaction (HER; − 0.24 V vs RHE at − 10 mA cm − 2 ), thus demonstrating that it is a good bi-functional ORR and HER catalyst in acidic media.

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Section: Thickness Of Carbon Shells For Orr Activitymentioning

confidence: 99%

Towards a comprehensive understanding of FeCo coated with N-doped carbon as a stable bi-functional catalyst in acidic media

et al. 2016

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“…The electrochemical stability of Pt atoms shown in Table 6 indicates that the Pt atoms are more stable on the alloy surfaces than on pure Pt (111) surfaces as shown by the positive shift in potentials on surfaces covered with 1/8 ML of O. The maximum values found for an intermediate amount of Ir suggests that further lowering the amounts of Ir in the alloy compositions may result in less stable surfaces due to the large lattice mismatch between Pt and transition metal atoms [17]. …”

mentioning

confidence: 88%

“…A series of Pt monolayer core shell materials have been successfully prepared using scaleable chemistries, on a range of core types, including [19] and also by modelling work on Pt ML /Pd 3 X [20] indicating segregation of Pd and X to the surface in the presence of adsorbed oxygen.…”

Section: Core-shell Catalystsmentioning

confidence: 99%

“…[22] Other derivations done at TAMU were peer reviewed and reported in a series of published articles. [20,27,28,29,30,31,32,33,34,35,36,37,16] f. Summary of theoretical strengths and weaknesses; As explained in (e), DFT methods and mathematical algorithms have been published by others. Modeling results of work performed under this program were published in peer-reviewed articles.…”

Section: Molecular Modelingmentioning

confidence: 99%

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Highly Dispersed Alloy Catalyst for Durability

Murthi¹,

Izzo²,

Bi³

et al. 2013

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OBJECTIVES Develop structurally and compositionally advanced supported alloy catalyst system with loading < 0.3 mg platinum group metal (PGM)/cm 2 . Optimize catalyst performance and decay parameters through quantitative models.  Demonstrate 5,000 cyclic hours below 80°C with less than 40% loss of electrochemical surface area and catalyst mass activity. TECHNICAL BARRIERSThis project addresses the following technical barriers from the Fuel Cells section (section 3.4. SUMMARYAchieving DOE's stated 5000-hr durability goal for light-duty vehicles by 2015 will require MEAs with characteristics that are beyond the current state of the art. Significant effort was placed on developing advanced durable cathode catalysts to arrive at the best possible electrode for high performance and durability, as well as developing manufacturing processes that yield significant cost benefit. Accordingly, the overall goal of this project was to develop and construct advanced MEAs that will improve performance and durability while reducing the cost of PEMFC stacks. The project, led by UTC Power, focused on developing new catalysts/supports and integrating them with existing materials (membranes and gas diffusion layers (GDLs)) using state-of-the-art fabrication methods capable of meeting the durability requirements essential for automotive applications. Specifically, the project work aimed to lower platinum group metals (PGM) loading while increasing performance and durability. Appropriate catalysts and MEA configuration were down-selected that protects the membrane, and the layers were tailored to optimize the movements of reactants and product water through the cell to maximize performance while maintaining durability. A brief summary of accomplishments from FY2008-FY2012 is provided below FY2008:The atomistic modeling work guiding the synthesis project was providing fundamental activity and durability controlling information. Preliminary samples synthesized on the project exceeded the DOE 2010 targets for mass activity when normalized to mass of Pt. However, further work is needed to achieve the PGM based mass activity targets. FY2009:Mass activities of almost 0. Pt ML catalyst prepared using scalable chemistries and characterized by a range of techniques showed strong evidence for a core-shell structure. However, a key challenge for the core-shell catalysts was their poor durability towards potential cycling due to non-uniform Pt layer on the core structures. Various scalable methods specifically geared towards achieving uniform Pt coatings were completed. FY2010:Mass activities of~0.15 A/mg PGM in subscale MEA testing have been reproduced and verified for a scaled-up 30% Pt 2 IrCr and was down-selected as the dispersed alloy catalyst system for full scale fuel cell demonstration. The Pt 2 IrCr alloy was chosen, over the PtIrCo alloy, based on the higher durability of Cr over Co in the alloy catalysts under the MEA fabrication process. Key barriers to overcome for the incorporation of the 30% Pt 2 IrCr in an MEA such as the low...

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“…Moreover, we note that the effect of the reduced lattice constant of the Ir-Co cores by the Pd interlayer clearly is reflected in the adsorption energies of the adsorbates. Ramírez-Caballero et al [37] To summarize, this section describes a simple method of improving Pt monolayer core-shell catalysts that have an inadequate Pt-core interaction causing their relatively low ORR activity. Using a Pd monolayer as an interlayer between Pt and the core modifies their interaction and improves their ORR activity significantly.…”

Section: Addition Of An Interlayer Between the Ptmentioning

confidence: 99%

Platinum Monolayer Electrocatalysts for the Oxygen Reduction Reaction: Improvements Induced by Surface and Subsurface Modifications of Cores

Cai

Adžić

2011

Advances in Physical Chemistry

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This paper demonstrates that the ORR activity of Pt ML electrocatalysts can be further improved by the modification of surface and subsurface of the core materials. The removal of surface low-coordination sites, generation (via addition or segregation) of an interlayer between Pt ML and the core, or the introduction of a second metal component to the subsurface layer of the core can further improve the ORR activity and/or stability of Pt ML electrocatalysts. These modifications generate the alternation of the interactions between the substrate and the Pt ML , involving the changes on both electronic (ligand) and geometric (strain) properties of the substrates. The improvements resulted from the application of these approaches provide a new perspective to designing of the new generation Pt ML electrocatalysts.

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Surface segregation and stability of core–shell alloy catalysts for oxygen reduction in acid medium

Cited by 119 publications

References 69 publications

Towards a comprehensive understanding of FeCo coated with N-doped carbon as a stable bi-functional catalyst in acidic media

Towards a comprehensive understanding of FeCo coated with N-doped carbon as a stable bi-functional catalyst in acidic media

Highly Dispersed Alloy Catalyst for Durability

Platinum Monolayer Electrocatalysts for the Oxygen Reduction Reaction: Improvements Induced by Surface and Subsurface Modifications of Cores

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