Selective Dissolution of Surface Nickel Close to Platinum in PtNi Nanocatalyst toward Oxygen Reduction Reaction

Jeon, Tae‐Yeol; Kim, Sang Kyung; Pinna, Nicola; Sharma, Aditya; Park, Jucheol; Lee, Su Yong; Lee, Hae Cheol; Kang, Seen-Woong; Lee, Han-Koo; Lee, Hyun Hwi

doi:10.1021/acs.chemmater.6b00103

Cited by 43 publications

(19 citation statements)

References 51 publications

(97 reference statements)

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“…Thus, it can be concluded that the surface of PtNi‐20 was Pt‐rich when the CO‐stripping was performed, indicating that the pristine Ni‐shell observed by HAADF‐STEM was leached in the electrolyte, exposing an “activated” surface of platinum. [ 41,42 ]…”

Section: Resultsmentioning

confidence: 99%

Octahedral to Cuboctahedral Shape Transition in 6 nm Pt₃Ni Nanocrystals for Oxygen Reduction Reaction Electrocatalysis

Zysler

Zitoun

2020

Part & Part Syst Charact

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this study), leads to difficulty producing scaled-up catalyst quantities sufficient for a PEMFC test.Extensive efforts have been carried out to obtain control on the shape, exposed facets, [7] and size of Pt-Ni bimetallic nanoparticles (NPs); [8][9][10][11] with different elemental composition, [12] surface composition, [13][14][15] and porosity [16] to enhance the ORR activity and durability with the lowest possible amount of Pt. Therefore, it is extremely important to design the synthesis of shape-controlled Pt-Ni NPs toward their potential use in cathode layers of PEMFCs. The syntheses of Pt-Ni NPs have explored a variety of metal precursors, [17] postsynthesis treatment, [18] and dealloying or etching processes [19][20][21][22][23][24] to yield the best electrocatalysts. The ability to tune the morphology by surfactantassisted synthesis [25] has been instrumental in enhancing the mass activity of polyhedral Pt-Ni NPs. The reaction mechanism of growth [26] and etching [27] has been scarcely reported.Solvothermal synthesis usually generates octahedral NPs with high ORR activity of the {111} facets and yield bimetallic nanoparticles with a Pt skeleton and a Ni-rich core. [28] Pt-Ni cuboctahedra nanocrystals with a high activity toward the same reaction have been reported. Cui et al. [13] have reported very high activities. Recently, a very high specific activity has been reported for a well-defined octahedral particle but the rather large particle size (10-15 nm) impedes the mass activity. [29] In this paper, we investigate the structure-properties relationship of Pt 3 Ni NPs with a particle size of 5-6 nm, which is close to the optimal value for ORR electrocatalysts and the lowest reported to still display shape and preferential crystallographic orientation of the facets. We show how a simple synthetic parameter, the ratio between the solution and the free volume in the reactor, leads to the formation of octahedral or cuboctahedral PtNi nanocrystals. Interestingly, each shape displays a different chemical ordering with Pt or Nirich surface, as evidenced by high-angle annular dark-field (HAADF)-high-resolution transmission electron microscopy (HRTEM) mapping. In the case of cuboctahedral NPs, after a few cyclic voltammograms in acidic medium, the NPs retain their geometry but display a Pt-rich skin which explains their ORR activity.Pt 3 Ni stands as one of the most active electrocatalysts for the oxygen reduction reaction (ORR). The activity varies with the morphology of the nanocrystals with a high activity observed for the octahedral shape where only the high density {111} crystallographic planes are exposed. Herein, the synthesis of 6 nm Pt 3 Ni octahedral nanocrystals with a Pt enriched shell or cuboctahedral nanocrystals with a Ni enriched shell is described. Interestingly, the cuboctahedral nanocrystals display a six-pointed star/skeleton of platinum, which features a very uncommon atomic distribution. In the synthesis, a decrease in the oxygen partial pressure induces the transition from octahedral to cub...

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Section: Resultsmentioning

confidence: 99%

Octahedral to Cuboctahedral Shape Transition in 6 nm Pt₃Ni Nanocrystals for Oxygen Reduction Reaction Electrocatalysis

Zysler

Zitoun

2020

Part & Part Syst Charact

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“…In contrast, HQ exhibited the opposite trend to SA, that is, higher CN Pt-O and CN Pt-Pt , lower CN Pt-Ni , values, highlighting that hydroquinone treatment leaves the largest domain size of Ptskin in the surface layer by selectively removing alloyed Ni atoms close to Pt. 25 The initial surface states before and after leaching surface Ni out using sulfuric acid and hydroquinone were illustrated in Figure 6. Both HQ and SA had higher surface Pt concentration than that of PR.…”

Section: Resultsmentioning

confidence: 99%

“…Here we report a study on the relationship between electrochemical properties and several factors related to surface structures in Pt 3 Ni/Pt 3+ x Ni 1− x core/shell nanocrystals, which were prepared using two different chemical solutions (sulfuric acid aqueous solution 24 or hydroquinone dissolved in ethanol 25 ) to leach out Ni at the surface. From the changes in electrochemical and structural properties of Pt‐enriched Pt 3 Ni, and commercial Pt occurring during 3000 potential cycles in oxygen‐saturated acidic aqueous solution, we first suggested that charge ratio for the oxidation of CO 26 and reduced CO 2 (“CO 2 ”) adlayers 27 can be one of the key indicators to describe surface structures as well as ORR activity at pristine and degraded states.…”

Section: Introductionmentioning

confidence: 99%

Electrochemical determination of the degree of atomic surface roughness in Pt–Ni alloy nanocatalysts for oxygen reduction reaction

Jeon

Yoo

et al. 2020

Carbon Energy

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Pt-Ni alloy nanocrystals with Pt-enriched shells were prepared by selective etching of surface Ni using sulfuric acid and hydroquinone. The changes in the electronic and geometric structure of the alloy nanoparticles at the surface were elucidated from the electrochemical surface area, the potential of zero total charge (PZTC), and relative surface roughness, which were determined from CO-and CO 2 -displacement experiments before and after 3000 potential cycles under oxygen reduction reaction conditions. While the highest activity and durability were achieved in hydroquinone-treated Pt-Ni, sulfuric acidtreated one showed the lower activity and durability despite its higher surface Pt concentration and alloying level. Both PZTC and Q CO 2 /Q CO ratio (desorption charge of reductively adsorbed CO 2 normalized by CO ad -stripping charge) depend on surface roughness. In particular, Q CO 2 /Q CO ratio change better reflects the roughness on an atomic scale, and PZTC is also affected by the electronic modification of Pt atoms in surface layers. In this study, a comparative study is presented to find a relationship between surface structure and electrochemical properties, which reveals that surface roughness plays a critical role to improve the electrochemical performance of Pt-Ni alloy catalysts with Pt-rich surfaces.

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“…The electrochemical de‐alloying method refers to the process where the less‐noble metal is selectively dissolved from the bimetallic surface via applied anodic current until a Pt‐rich surface or shell is formed . The de‐alloying process can also be achieved by acid leaching . The under potential deposition method utilizes the phenomenon that only one layer of Cu can be deposited on a noble metal surface, such as Pt or Pd, under the equilibrium reduction potential .…”

Section: Practical Methods To Enhance Orr Activitymentioning

confidence: 99%

Enhancing Oxygen Reduction Activity of Pt‐based Electrocatalysts: From Theoretical Mechanisms to Practical Methods

et al. 2020

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Pt‐based electrocatalysts are considered as one of the most promising choices to facilitate the oxygen reduction reaction (ORR), and the key factor enabling their success is to reduce the required amount of platinum. Herein, we focus on illuminating both the theoretical mechanisms which enable enhanced and sustained ORR activity and the practical methods to achieve them in catalysts. The various multi‐step pathways of ORR are firstly reviewed and the rate‐determining steps based on the reaction intermediates and their binding energies are analyzed. We then explain the critical aspects of Pt‐based electrocatalysts to tune oxygen reduction properties from the viewpoints of active sites exposure and altering the surface electronic structure, and further summarize representative research progress towards practically achieving these activity enhancements with a focus on platinum size reduction, shape control and core Pt elimination methods. We finally outline the remaining challenges and provide our perspectives with regard to further enhancing their activities.

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Selective Dissolution of Surface Nickel Close to Platinum in PtNi Nanocatalyst toward Oxygen Reduction Reaction

Cited by 43 publications

References 51 publications

Octahedral to Cuboctahedral Shape Transition in 6 nm Pt₃Ni Nanocrystals for Oxygen Reduction Reaction Electrocatalysis

Octahedral to Cuboctahedral Shape Transition in 6 nm Pt₃Ni Nanocrystals for Oxygen Reduction Reaction Electrocatalysis

Electrochemical determination of the degree of atomic surface roughness in Pt–Ni alloy nanocatalysts for oxygen reduction reaction

Enhancing Oxygen Reduction Activity of Pt‐based Electrocatalysts: From Theoretical Mechanisms to Practical Methods

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Selective Dissolution of Surface Nickel Close to Platinum in PtNi Nanocatalyst toward Oxygen Reduction Reaction

Cited by 43 publications

References 51 publications

Octahedral to Cuboctahedral Shape Transition in 6 nm Pt3Ni Nanocrystals for Oxygen Reduction Reaction Electrocatalysis

Octahedral to Cuboctahedral Shape Transition in 6 nm Pt3Ni Nanocrystals for Oxygen Reduction Reaction Electrocatalysis

Electrochemical determination of the degree of atomic surface roughness in Pt–Ni alloy nanocatalysts for oxygen reduction reaction

Enhancing Oxygen Reduction Activity of Pt‐based Electrocatalysts: From Theoretical Mechanisms to Practical Methods

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Octahedral to Cuboctahedral Shape Transition in 6 nm Pt₃Ni Nanocrystals for Oxygen Reduction Reaction Electrocatalysis

Octahedral to Cuboctahedral Shape Transition in 6 nm Pt₃Ni Nanocrystals for Oxygen Reduction Reaction Electrocatalysis