Activity Descriptor Identification for Oxygen Reduction on Platinum-Based Bimetallic Nanoparticles: <i>In Situ</i> Observation of the Linear Composition–Strain–Activity Relationship

Jia, Qingying; Liang, Wentao; Bates, Michael K.; Mani, Prasanna; Lee, Wendy; Mukerjee, Sanjeev

doi:10.1021/nn506721f

Cited by 165 publications

(204 citation statements)

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“…This compressive strain is comparable to that observed by Jia et al for a Pt 3 Co nanoparticle catalyst. 56 As discussed in the introduction and extensively in the literature, the enhanced ORR activity of Pt alloys versus Pt has been attributed to the compressive strain of surface Pt induced by the underlying alloying elements. 56 As shown in Figure 13 and as was also observed by Jia et al, potential cycling the Pt 3 Co catalyst in either the aqueous or MEA environment increased the Pt-Pt bond distances, decreasing the compressive strain, which can cause decreased ORR area-specific activity.…”

Section: Resultsmentioning

confidence: 99%

In-Operando Anomalous Small-Angle X-Ray Scattering Investigation of Pt₃Co Catalyst Degradation in Aqueous and Fuel Cell Environments

Gilbert

Kropf

Kariuki

et al. 2015

J. Electrochem. Soc.

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Platinum-cobalt alloy nanoparticles are of great interest as cathode catalysts for PEMFCs as they have been shown to have enhanced activity versus platinum. However, their relative stability against loss of electrochemically-active surface area in relation to Pt catalysts is still debated. In this study, the evolutions of Pt 3 Co particle size distributions (PSDs) in fuel cell and aqueous environments were followed during accelerated stress tests (ASTs) using in-operando ASAXS. The measured evolutions showed a degradation mechanism dominated by loss of particles smaller than the critical particle diameter (<5.2 to 6.1 nm, CPD), which depended on environment and the AST. These evolutions were compared to that of a Pt catalyst with a similar initial PSD, which was found to have a lower degradation rate than Pt 3 Co. The ASAXS data, as well as data from aqueous dissolution, X-ray absorption spectroscopy, individual particle energy-dispersive spectroscopy, X-ray fluorescence spectrometry, and kinetic Monte Carlo calculations support a loss mechanism of increased Pt dissolution from Pt 3 Co versus Pt due to destabilization caused by extensive dealloying of particles <∼5 nm during ASTs. Polymer electrolyte fuel cells (PEFCs) are a promising highefficiency energy conversion technology suitable for mobile and stationary applications. Two of the major issues still needing to be addressed for large-scale adoption are cost and durability. The major contributing factor to these issues is the electrocatalyst needed for the cathodic oxygen reduction reaction (ORR). Pt has been shown to be the best monometallic catalyst material for ORR 1 with high activity and good stability in the acidic environment of the PEFC.2,3 However, there is still a need for a more active, more stable, and less expensive cathode electrocatalyst to meet the demanding cost and lifetime requirements for many applications, especially for automotive propulsion power.Pt alloys are of great interest as ORR electrocatalysts as they are generally less expensive and have been shown to have enhanced activity versus Pt. [4][5][6] This enhancement in activity was found to be directly correlated with the Pt-Pt interatomic distance 7,8 and to the Pt d-band occupancy in the alloy. [8][9][10] However, there are concerns that the use of base metal alloying elements, which are generally less stable than Pt in acidic environments, could be accompanied by a loss in particle stability and corresponding loss in ORR activity. Conflicting reports exist about the overall stability of Pt alloy catalysts in relation to pure Pt catalysts. 5,6,[11][12][13] Some studies suggest that alloying has a positive effect while others show no significant impact on stability. It is known that relative stability is dependent on particle size, 14-16 the larger the initial particle size the more stable, and the majority of Pt alloy synthesis techniques are based on high temperature annealing processes which result in larger initial particle sizes. Therefore any comparisons between larger annea...

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Section: Resultsmentioning

confidence: 99%

In-Operando Anomalous Small-Angle X-Ray Scattering Investigation of Pt₃Co Catalyst Degradation in Aqueous and Fuel Cell Environments

Gilbert

Kropf

Kariuki

et al. 2015

J. Electrochem. Soc.

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“…In recent years, bimetallic nanoparticles have received increasing attention due to their promising electrocatalytic, [1][2][3] catalytic, [4][5][6][7][8] magnetic, 4,9,10 and optical properties. 4,11 The interaction of nanoparticles with their environment can, sometimes drastically, shift the Fermi level of electrons in the nanoparticles, influencing their chemical and electrochemical properties, as highlighted in a recent review.…”

Section: Introductionmentioning

confidence: 99%

Charge distribution and Fermi level in bimetallic nanoparticles

Holmberg

Laasonen

Peljo

2016

Phys. Chem. Chem. Phys.

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Upon metal-metal contact, a transfer of electrons will occur between the metals until the Fermi levels in both phases are equal, resulting in a net charge difference across the metal-metal interface. Here, we have examined this contact electrification in bimetallic model systems composed of mixed Au-Ag nanoparticles containing ca. 600 atoms using density functional theory calculations. We present a new model to explain this charge transfer by considering the bimetallic system as a nanocapacitor with a potential difference equal to the work function difference, and with most of the transferred charge located directly at the contact interface. Identical results were obtained by considering surface contacts as well as by employing a continuum model, confirming that this model is general and can be applied to any multimetallic structure regardless of geometry or size (going from nano-to macroscale). Furthermore, the equilibrium Fermi level was found to be strongly dependent on the surface coverage of different metals, enabling the construction of scaling relations. We believe that the charge transfer due to Fermi level equilibration has a profound effect on the catalytic, electrocatalytic and other properties of bimetallic particles. Additionally, bimetallic nanoparticles are expected to have very interesting self-assembly for large superstructures due to the surface charge anisotropy between the two metals.

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“…The major advantage of this strategy is that the electrode was cycled in a practical PEMFC rather than in a half-cell, and thus provides more relevant spectroscopic data to the degradation in PEMFCs. 9 However, no XAS signals were detected at both the Pt and Co edges. On the other hand, the XAS spectra of the membrane are close to those of the single-sided MEA (Figure 3).…”

Section: Resultsmentioning

confidence: 99%

“…In addition, XAS is extremely suitable for understanding the structural and mechanistic basis of the ORR activity and durability of PtM/C electrocatalysts since it allows for quantitative evaluation of the strain, ligand, particle size, and site-blocking effects on their catalytic performance. 5,6,[9][10][11] Therefore, substantial efforts have been devoted to actualizing in situ/operando XAS characterization of PtM/C NPs cycled in PEMFCs to obtain the structure-activity-durability correlations. 12,13 An operando XAS fuel cell was built wherein the MEA was composed of a cathode electrode of PtNi/C NPs subject to XAS characterization, and an anode electrode of Pd/C NPs (the Pt/C NPs cannot be used due to the convolution of the Pt signals from the Pt/C and the PtNi/C).…”

mentioning

confidence: 99%

Actualizing In Situ X-ray Absorption Spectroscopy Characterization of PEMFC-Cycled Pt-Electrodes

Miller

Davies

et al. 2018

J. Electrochem. Soc.

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The family of the PtM (M represents transition metals such as Co, Ni, Pd, etc.) alloys is the most promising cathode electrocatalysts for proton exchange membrane fuel cells (PEMFCs) owing to their superior oxygen reduction reaction (ORR) activity to pure Pt. However, the activity gain fades with long-term PEMFC operation, and the degradation mechanism is not yet fully understood. To truly understand the degradation mechanism of the carbon supported PtM nanoparticles (PtM/C) in the cathode of a membrane electrode assembly (MEA) upon long-term PEMFC operation, it is essential to characterize the PEMFC-cycled electrode under working conditions. Herein, we showed that operando X-ray absorption spectroscopy (XAS) characterization of PtM/C electrocatalysts cycled in a PEMFC has inherent difficulties since Pt and especially M dissolve during PEMFC operation and migrate into the membrane; the bulk XAS spectrum is an average of the signals from the electrode and the membrane. Alternatively, we developed a method that allows for in situ XAS characterization on PEMFC-cycled PtM/C electrocatalysts. We justified the method by showing that the dissolved species in the membrane were separated from the PtM/C electrocatalyst in the cathode, and the in situ XAS signals arose exclusively from the electrocatalyst. Despite recent progress in the development of non-platinum electrocatalysts for the oxygen reduction reaction (ORR), carbon supported platinum-based nanoparticles (NPs) are still so far the only viable electrocatalysts for practical proton exchange membrane fuel cells (PEMFCs) in automotive vehicles, owing to their high activity and durability under the highly oxidative and corrosive conditions in the cathode of a PEMFC. The ORR activity of platinum can be significantly improved by alloying Pt with a wide range of transition metals (denoted as M) such as Co, Ni, Y, and the activity improvement has been attributed to the strain and/or ligand effects induced by M via optimization of the Pt-O binding energy and surface coordinate configuration. 1-5 However, the activity gain induced by M is generally not sustainable owing primarily to the dissolution of M during long-term PEMFC operation, which leads to the attenuation of strain/ligand effects, particle growth, and the loss of the favorable surface coordinate configuration. 6 Huang et al. 7 recently reported that both the activity and durability of the PtNi/C octahedral NPs can be markedly improved by doping with a transition metal such as Mo on the surface. However, neither the degradation mechanism of the PtM/C electrocatalysts during long-term PEMFC operation, nor the corresponding alleviation mechanism, is fully understood, which limits further improvements of the PtM/C electrocatalysts for PEMFCs.Elucidating the degradation mechanism of the PtM/C electrocatalysts during long-term PEMFC operation is technically challenging as it requires proper electrochemical testing methods and characterization methods, and a combination thereof. A regular way is to potentially cycle ...

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Activity Descriptor Identification for Oxygen Reduction on Platinum-Based Bimetallic Nanoparticles: In Situ Observation of the Linear Composition–Strain–Activity Relationship

Cited by 165 publications

References 72 publications

In-Operando Anomalous Small-Angle X-Ray Scattering Investigation of Pt₃Co Catalyst Degradation in Aqueous and Fuel Cell Environments

In-Operando Anomalous Small-Angle X-Ray Scattering Investigation of Pt₃Co Catalyst Degradation in Aqueous and Fuel Cell Environments

Charge distribution and Fermi level in bimetallic nanoparticles

Actualizing In Situ X-ray Absorption Spectroscopy Characterization of PEMFC-Cycled Pt-Electrodes

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Activity Descriptor Identification for Oxygen Reduction on Platinum-Based Bimetallic Nanoparticles: In Situ Observation of the Linear Composition–Strain–Activity Relationship

Cited by 165 publications

References 72 publications

In-Operando Anomalous Small-Angle X-Ray Scattering Investigation of Pt3Co Catalyst Degradation in Aqueous and Fuel Cell Environments

In-Operando Anomalous Small-Angle X-Ray Scattering Investigation of Pt3Co Catalyst Degradation in Aqueous and Fuel Cell Environments

Charge distribution and Fermi level in bimetallic nanoparticles

Actualizing In Situ X-ray Absorption Spectroscopy Characterization of PEMFC-Cycled Pt-Electrodes

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Product

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In-Operando Anomalous Small-Angle X-Ray Scattering Investigation of Pt₃Co Catalyst Degradation in Aqueous and Fuel Cell Environments

In-Operando Anomalous Small-Angle X-Ray Scattering Investigation of Pt₃Co Catalyst Degradation in Aqueous and Fuel Cell Environments