The Role of Citric Acid in Perfecting Platinum Monolayer on Palladium Nanoparticles during the Surface Limited Redox Replacement Reaction

Zhu, Shangqian; Yue, Jeffrey; Qin, Xueping; Wei, Zidong; Liang, Zhixiu; Adžić, Radoslav R.; Brankovic, Stanko R.; Du, Zheng; Shao, Minhua

doi:10.1149/2.0061612jes

Cited by 19 publications

(14 citation statements)

References 27 publications

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“…In terms of shell thickness, a monolayer is in theory ideal and has been elaborately achieved through the use of different methods including the UPD, the ALD and the sputtering deposition, exhibiting better catalytic activities for ORRs than pure Pt due to strain and ligand effects [45,59,65,66,299,301,304,334]. However, experimental results have indicated that optimum Pt thicknesses involve 2~3 atomic layers, rather than the monolayer for catalytic performances [297,299,409,410]. For example, a Pd@Pt catalyst with a two atomic layer shell was found to exhibit a higher mass activity normalized by the mass of Pt and Pt-group metals (MA P , MA PGM ) and a higher specific activity (SA) than catalysts with a monolayer shell [297,409].…”

Section: Pd As Corementioning

confidence: 99%

Core–Shell-Structured Low-Platinum Electrocatalysts for Fuel Cell Applications

Wang

Luo

et al. 2018

Electrochem. Energ. Rev.

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Pt-based catalysts are the most efficient catalysts for low-temperature fuel cells. However, commercialization is impeded by prohibitively high costs and scarcity. One of the most effective strategies to reduce Pt loading is to deposit a monolayer or a few layers of Pt over other metal cores to form core-shell-structured electrocatalysts. In core-shell-structured electrocatalysts, the compositions of the core can be divided into five classes: single-precious metallic cores represented by Pd, Ru, and Au; singlenon-precious metallic cores represented by Cu, Ni, Co, and Fe; alloy cores containing 3d, 4d or 5d metals; and carbide and nitride cores. Of these, researchers have found that carbide and nitride cores can yield tremendous advantages over alloy cores in terms of cost and promotional activities of Pt shells. In addition, desirable shells with reasonable thicknesses and compositions have been recognized to play a dominant role in electrocatalytic performances. And recently, researchers have also found that the catalytic activity of core-shell-structured catalysts is dependent on the binding energy of the adsorbents, which is determined by the d-band center of Pt. The shifting of this d-band center in turn is mainly affected by strain and electronic effects, which can be adjusted by adjusting core compositions and shell thicknesses of catalysts. In the development of these core-shell structures, optimal synthesis methods are of primary concern because they directly determine the practical application potential of the resulting electrocatalysts. And in this article, the principles behind core-shell-structured low-Pt electrocatalysts and the developmental progresses of various synthesis methods along with the traits of each type of core and its effects on Pt shell catalytic activities are discussed. In addition, perspectives on this type of catalyst are discussed and future research directions are proposed.

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Section: Pd As Corementioning

confidence: 99%

Core–Shell-Structured Low-Platinum Electrocatalysts for Fuel Cell Applications

Wang

Luo

et al. 2018

Electrochem. Energ. Rev.

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“…Most of their work focused on the use of these catalysts as efficient oxygen reduction cathodes, although they also studied them as alcohol and CO anodes as well. They were the first to scale up this preparation route to practical carbon-supported catalysts [90], soon followed by other work [53,98,99]. On the other hand, Sotiropoulos and co-workers continued the partial galvanic replacement of metal poly-layers (Cu, Pb, Fe, Co, Ni) by more noble metals (mainly Pt, Au, Ru, Ir) and used the resulting electrodes in a number of fuel cell and electrolysis relevant reactions (oxygen reduction, methanol oxidation, borohydride oxidation, hydrogen and oxygen evolution) [67,68,[100][101][102][103][104][105][106][107][108][109][110][111][112][113].…”

Section: Nanoparticle and Catalytic Layer Applicationsmentioning

confidence: 99%

Electrocatalysts Prepared by Galvanic Replacement

et al. 2017

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Galvanic replacement is the spontaneous replacement of surface layers of a metal, M, by a more noble metal, M noble , when the former is treated with a solution containing the latter in ionic form, according to the general replacement reaction: nM + mM noble n+ → nM m+ + mM noble. The reaction is driven by the difference in the equilibrium potential of the two metal/metal ion redox couples and, to avoid parasitic cathodic processes such as oxygen reduction and (in some cases) hydrogen evolution too, both oxygen levels and the pH must be optimized. The resulting bimetallic material can in principle have a M noble-rich shell and M-rich core (denoted as M noble (M)) leading to a possible decrease in noble metal loading and the modification of its properties by the underlying metal M. This paper reviews a number of bimetallic or ternary electrocatalytic materials prepared by galvanic replacement for fuel cell, electrolysis and electrosynthesis reactions. These include oxygen reduction, methanol, formic acid and ethanol oxidation, hydrogen evolution and oxidation, oxygen evolution, borohydride oxidation, and halide reduction. Methods for depositing the precursor metal M on the support material (electrodeposition, electroless deposition, photodeposition) as well as the various options for the support are also reviewed. 1. Principle of Galvanic Replacement/Deposition 1.1. Thermodynamic Considerations When a metal, M (e.g., Cu, Fe, Co, Ni, Al, etc.), is immersed in a solution containing ions of a more noble metal, M noble n+ (e.g., Pt, Au, Pd, Ag, Ru, Ir, Rh, Os, etc.-i.e., a metal with a higher standard potential) then, due to the difference in their standard electrochemical potentials, E 0 noble − E 0 > 0, and provided that the ionic form of M is stable under the given experimental conditions (of temperatue, pH, complexing agents etc.), the following reaction is thermodynamically favored and can take place spontaneously: M noble n+ + n/m M → M noble + n/m M m+ (1) This reaction, which bears similarities with transmetalation reactions between metal complexes [1] and is also known as immersion plating [2] in the plating industry and galvanic replacement [3] in materials chemistry, can be considered to originate from the coupling of the following two half-reactions: M noble n+ + ne − ↔ M noble (E 0 noble) (2) M m+ + me − ↔ M (E 0) (3)

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“…The role of citric acid in controlling the uniformity of Pt monolayers on Pd was studied by electrochemical techniques and theoretical approaches 53 . It was found that citric acid strongly adsorbed on Pd, Pt, Cu@Pd (Cu UPD layer) and Pd@Pt surfaces, especially in the double layer region in acid solutions.…”

Section: Gram Batch Synthesismentioning

confidence: 99%

“…The durability of core-shell electrocatalysts were evaluated on RDE using a square-wave signal between 0.65 and 1.00 V for 5 s at each potential. After 10000 cycles, the Pt mass activity of Pd@Pt/C dropped by 16% 53 . This result suggested that Pd@Pt/C was even more stable than Pt/C, which degraded 42% under the same testing condition.…”

Section: Gram Batch Synthesismentioning

confidence: 99%

Core-Shell Electrocatalysts for Oxygen Reduction Reaction

Chang¹,

Xiao²,

Xu³

et al. 2017

Acta Physico-Chimica Sinica

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The high cost of platinum in catalyst layers hinders the commercialization of proton exchange membrane fuel cells. This Account reviews recent progress on core-shell nanostructures for oxygen reduction reaction (ORR) in acidic media, which is the cathodic reaction in fuel cells. The synthesis, characterization and evaluation of different types of core-shell electrocatalysts are summarized. Various strategies to improve the performance of core-shell electrocatalysts, including dealloying, morphology control, and surface modification are presented. The issues of mass production and fuel cell performance of core-shell electrocatalysts are also discussed.

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The Role of Citric Acid in Perfecting Platinum Monolayer on Palladium Nanoparticles during the Surface Limited Redox Replacement Reaction

Cited by 19 publications

References 27 publications

Core–Shell-Structured Low-Platinum Electrocatalysts for Fuel Cell Applications

Core–Shell-Structured Low-Platinum Electrocatalysts for Fuel Cell Applications

Electrocatalysts Prepared by Galvanic Replacement

Core-Shell Electrocatalysts for Oxygen Reduction Reaction

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