Monodisperse Pt<sub>3</sub>Co Nanoparticles as a Catalyst for the Oxygen Reduction Reaction: Size-Dependent Activity

Wang, Chao; Vliet, Dennis Van; Chang, Kee‐Chul; You, Hoydoo; Strmčnik, Dušan; Schlueter, John A.; Marković, Nenad M.; Stamenković, Vojislav R.

doi:10.1021/jp908203p

Cited by 196 publications

(206 citation statements)

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“…Wang, C., et al [7] observed a similar activity enhancement after annealing and attributes it to element segregation that results in a Pt enriched surface over a Ni enriched subsurface. This results in an activity enhancement originating from modifying the Pt surface atoms' electronic structure and adsorption properties by the subsurface transition metal atoms.…”

Section: Resultsmentioning

confidence: 77%

“…Overpotentials for the ORR [5], however, limit the efficiency of the PEMFC and contribute to a high system cost. Research addressing the low activity of Pt electrocatalysts has focused on developing Pt alloys primarily with transition metals [5], with special attention to Co [6,7] and Ni [2,8] Pt alloys. Stability studies on Pt-alloys have led to the theory that the outer layer of the Pt alloy nanoparticles undergoes segregation and dealloying steps where the particles develop a highly active Pt monolayer on top of the alloy core.…”

Section: Introductionmentioning

confidence: 99%

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Pt and Pt/Ni "Needle" Eletrocatalysts on Carbon Nanotubes with High Activity for the ORR

Elvington

Colón-Mercado

2011

Electrochemical and Solid-State Letters

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Section: Resultsmentioning

confidence: 77%

Section: Introductionmentioning

confidence: 99%

Pt and Pt/Ni "Needle" Eletrocatalysts on Carbon Nanotubes with High Activity for the ORR

Elvington

Colón-Mercado

2011

Electrochemical and Solid-State Letters

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“…In aqueous environments, the rotating disk electrode (RDE) measurements found that polycrystalline Pt3Co with a Pt skin has ORR specific activity three times greater than pure Pt, and Pt3Ni(111) has the highest ORR specific activity recorded to date with an enhancement factor of nearly twenty versus polycrystalline Pt [2,4,5]. Additionally, in RDE measurements, carbon-supported nanoparticles of Pt3Co with a mean diameter of 6 nm showed an ORR specific activity enhancement factor of three versus 6 nm mean diameter Pt [6]. Paulus et al found that Pt based alloy catalysts exhibit higher ORR specific activity than pure Pt by an enhancement factor of approximately 1.5 for bulk electrodes, 1.5 to 2 for supported Pt3X catalysts, and 2 to 3 for PtCo catalyst [7].…”

Section: Introductionmentioning

confidence: 97%

Effect of Particle Size and Operating Conditions on Pt3Co PEMFC Cathode Catalyst Durability

et al. 2015

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Abstract:The initial performance and decay trends of polymer electrolyte membrane fuel cells (PEMFC) cathodes with Pt3Co catalysts of three mean particle sizes (4.9 nm, 8.1 nm, and 14.8 nm) with identical Pt loadings are compared. Even though the cathode based on 4.9 nm catalyst exhibited the highest initial electrochemical surface area (ECA) and mass activity, the cathode based on 8.1 nm catalyst showed better initial performance at high currents. Owing to the low mass activity of the large particles, the initial performance of the 14.8 nm Pt3Co-based electrode was the lowest. The performance decay rate of the electrodes with the smallest Pt3Co particle size was the highest and that of the largest Pt3Co particle size was lowest. Interestingly, with increasing number of decay cycles (0.6 to 1.0 V, 50 mV/s), the relative improvement in performance of the cathode based on 8.1 nm Pt3Co over the 4.9 nm Pt3Co increased, owing to better stability of the 8.1 nm catalyst. The electron OPEN ACCESSCatalysts 2015, 5 927 microprobe analysis (EMPA) of the decayed membrane-electrode assembly (MEA) showed that the amount of Co in the membrane was lower for the larger particles, and the platinum loss into the membrane also decreased with increasing particle size. This suggests that the higher initial performance at high currents with 8.1 nm Pt3Co could be due to lower contamination of the ionomer in the electrode. Furthermore, lower loss of Co from the catalyst with increased particle size could be one of the factors contributing to the stability of ECA and mass activity of electrodes with larger cathode catalyst particles. To delineate the impact of particle size and alloy effects, these results are compared with prior work from our research group on size effects of pure platinum catalysts. The impact of PEMFC operating conditions, including upper potential, relative humidity, and temperature on the alloy catalyst decay trends, along with the EMPA analysis of the decayed MEAs, are reported.

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“…A catalyst with a Pt:Co atomic ratio of 3:1 was chosen for this study, as this ratio has been shown to have both the highest ORR activity and activity stability. 10,[30][31][32] This information combined with data obtained from transmission electron microscopy (TEM), individual particle energy-dispersive X-ray spectroscopy (EDS), X-ray fluorescence spectrometry (XRF), and extended X-ray absorption fine structure spectroscopy (EXAFS) provides insight into the degradation mechanism of Pt 3 Co and its relative durability to a similar-sized Pt electrocatalyst. …”

mentioning

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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Monodisperse Pt₃Co Nanoparticles as a Catalyst for the Oxygen Reduction Reaction: Size-Dependent Activity

Cited by 196 publications

References 40 publications

Pt and Pt/Ni "Needle" Eletrocatalysts on Carbon Nanotubes with High Activity for the ORR

Pt and Pt/Ni "Needle" Eletrocatalysts on Carbon Nanotubes with High Activity for the ORR

Effect of Particle Size and Operating Conditions on Pt3Co PEMFC Cathode Catalyst Durability

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

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Monodisperse Pt3Co Nanoparticles as a Catalyst for the Oxygen Reduction Reaction: Size-Dependent Activity

Cited by 196 publications

References 40 publications

Pt and Pt/Ni "Needle" Eletrocatalysts on Carbon Nanotubes with High Activity for the ORR

Pt and Pt/Ni "Needle" Eletrocatalysts on Carbon Nanotubes with High Activity for the ORR

Effect of Particle Size and Operating Conditions on Pt3Co PEMFC Cathode Catalyst Durability

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

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Monodisperse Pt₃Co Nanoparticles as a Catalyst for the Oxygen Reduction Reaction: Size-Dependent Activity

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