Platinum Nanofilm Formation by EC-ALE via Redox Replacement of UPD Copper:  Studies Using in-Situ Scanning Tunneling Microscopy

Kim, Youn-Geun; Kim, Jay Y.; Vairavapandian, Deepa; Stickney, John L.

doi:10.1021/jp063766f

Cited by 145 publications

(199 citation statements)

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“…In situ scanning tunneling microscopy (STM) was used to study the structure of Pt submonolayers. 8 Brankovic et al systematically studied the reaction mechanism of SLRR to replace the UPD Cu with Pt. They proposed a kinetic model, 16 based on the stoichiometry of SLRR, 6 and also proposed the nucleation mechanism of the Pt monolayer clusters, 17 and the UPD procedure on the Pt monolayer modified surface.…”

mentioning

confidence: 99%

Polarization-dependent Total Reflection Fluorescence X-ray Absorption Fine Structure (PTRF-XAFS) Studies on the Structure of a Pt Monolayer on Au(111) Prepared by the Surface-limited Redox Replacement Reaction

et al. 2017

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We studied the initial stage of a Pt monolayer produced by surface-limited redox replacement (SLRR) using polarizationdependent total reflection fluorescence X-ray absorption fine structure (PTRF-XAFS). Different from the widely accepted understanding that metallic monolayer islands are formed, our XAFS showed that the Pt monolayer, initially present on the Au(111) substrate, was mainly in the form of a planar [PtCl 4 ] 2¹ complex with its molecular plane parallel to Au(111). This result provides a new insight into the mechanism of SLRR.Keywords: X-ray absorption fine structure (XAFS) | Surface-limited redox replacement reaction | Pt monolayerPolymer electrolyte fuel cells (PEFCs), which emit no greenhouse gases, have attracted much attention because of the necessity for the modern society to shift from fossil fuels to clean energy. However, several issues concerning electrocatalysts, including their cost and durability, have greatly inhibited the practical use of PEFCs.1 To reduce the cost of the electrocatalyst, we need to increase the surface area of Pt, which is the main component of the fuel cell catalyst currently. Considerable effort has been devoted to investigating the electrodeposition of Pt. 24Owing to the high surface energy and low wettability of Pt, it is difficult to obtain monolayer deposition on a flat surface with conventional electrodeposition methods.2,4 Brankovic et al. developed a method for Pt monolayer deposition by galvanic displacement of a layer of sacrificial underpotential deposition (UPD) metal, which is called surface-limited redox replacement (SLRR).5 Several sacrificial materials, like Cu, 68 Pb,7,9 and H,10 have been studied for the deposition of Pt monolayers. In addition to Pt, the SLRR was extended to the monolayer deposition of other metals, such as Pd, 11 Ru, 12 and Ag. 5,13 Furthermore, bimetallic monolayer depositions were also achieved by the SLRR.14,15 However, there are only limited numbers of studies regarding the mechanism of the deposition process on atomic levels. In situ scanning tunneling microscopy (STM) was used to study the structure of Pt submonolayers.8 Brankovic et al. systematically studied the reaction mechanism of SLRR to replace the UPD Cu with Pt. They proposed a kinetic model, 16 based on the stoichiometry of SLRR, 6 and also proposed the nucleation mechanism of the Pt monolayer clusters, 17 and the UPD procedure on the Pt monolayer modified surface. 9,15 However, some aspects remain unclear. For example, what is the chemical state and structure of the Pt submonolayers and Pt submonolayerAu interaction, which are very important parameters since they are related to the catalytic properties? To examine the Pt initial structure created by the SLRR of the Cu UPD layer, we applied polarization-dependent total reflection fluorescence-X-ray absorption fine structure (PTRF-XAFS) techniques. 1820PTRF-XAFS is a powerful way of characterizing the surface structure and electronic state of less than a monolayer of adsorbate on atomically flat surfaces even und...

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confidence: 99%

Polarization-dependent Total Reflection Fluorescence X-ray Absorption Fine Structure (PTRF-XAFS) Studies on the Structure of a Pt Monolayer on Au(111) Prepared by the Surface-limited Redox Replacement Reaction

et al. 2017

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“…[22][23][24][25][26][27][28] In particular, potentiostatic routes can further be categorized as involving: (i) Overpotential Deposition (OPD), where a potential E M z+ /M is applied to a conductive substrate to drive reductive reaction, nucleation and growth of a solid metal phase from its corresponding metal ions, effectively with E M z+ /M more negative than the equilibrium potential, E eq , of the underlying reaction; and (ii) Underpotential Deposition (UPD) whereby deposition of adatoms of a metal takes place on a foreign metal substrate at potentials that are more positive than E eq of the metal ion deposition on its own metal surface, typically 6 producing sub-monolayer to monolayer phases of the metal. 29 [34][35][36] Moreover, overpotentially-deposited Ni bilayers through SLRR reactions involving Pt on polycrystalline Au was demonstrated to be just as effective as UPD based SLRR in deposition of Pt films. 37 Strasser and coworkers have explored an electrosynthetic methodology to generate core-shell type of nanomaterials (dealloyed electrocatalysts) by selective dissolution of a less noble metal such as Cu, by means of an applied potential, from a bimetallic alloy such as Pt x Cu 1-x , proposing that some kind of competition between the dissolution process and surface diffusion of the constituent metals results in a three dimensional metal removal and restructuring of atoms inside the bulk of the alloy.…”

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confidence: 99%

Multilayered Nanoclusters of Platinum and Gold: Insights on Electrodeposition Pathways, Electrocatalysis, Surface and Bulk Compositional Properties

Mkwizu

Mathe

Cukrowski

2013

J. Electrochem. Soc.

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and surface-to-near surface distribution of Pt and Au appeared to be influenced by the stoichiometry of the surface redox-replacement reactions and sequential dealloying processes through which the nanoclusters were synthesized. Interactions between metal centers, carbon and oxygen containing surface functional groups on the glassy carbon appeared to have played a significant role in the overall stabilization and catalytic activity of the nanoclusters. Profound effects were also found on interfacial charge-transfer and adsorptive properties involving carbon monoxide and its subsequent electrooxidation to CO 2 , as well as on the electrocatalytic activity involving formic acid oxidation reaction, where the Pt-rich (Pt|Au) exhibited the highest activity.3

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“…The NPG can be further functionalized with Pt by surface-limited redox replacement (SLRR) 12 to form Pt-NPG, and then applied as the catalyst in the formic acid oxidation and other catalytically relevant reactions. 7 Found to emphasize the enhanced activity boosted by synergism between Pt and Au, 13,14 Pt-NPG was constitutes a cost-effective alternative to Pt or Pt-Au core-shell nanoparticles. 7 Fabricated on Au and glassy carbon (GC) substrates the Pt-NPG catalyst features high mass activity (1-3 A mg −1 of combined Au + Pt catalyst) and a satisfactory performance in stability tests (2600 standard formic acid oxidation cycles).…”

Section: Npg Based Catalyst On Glassy Carbon (Gc)mentioning

confidence: 99%

Enhanced Adhesion of Ultrathin Nanoporous Au Deposits by Electrochemical Oxidation of Glassy Carbon

Xia

Rooney

Ambrozik

et al. 2015

J. Electrochem. Soc.

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Electrochemical (EO) and Thermochemical (TO) oxidation have been considered as means for improved adhesion of metals to glassy carbon (GC) substrates. This paper is aimed at studying the effect of EO on the all-electrochemical processing of nanoporous gold (NPG) catalysts with emphasis on their adhesion to a GC substrate. It has been shown by two independent assessment approaches that EO improves twice the amount of retained NPG on GC helping to keep about 90% originally existing material after a two-hour rotation disk electrode test at 1600 rpm. This work also demonstrates that EO modifies the GC in a way making it more passive in the alloy deposition and subsequent dealloying processes. This effect results in a progressive nucleation density decrease with the depth of oxidation which in turn leads to a lack of continuity of the NPG layer. This trend is also accompanied by a decrease in deposition efficiency as a substantial part of the cathodic current is spent on the reduction of the pre-oxidized GC surface. Our study identifies the best outcome of the trade-off scenario between nucleation density, deposition efficiency and adhesion strength to be associated with depth of oxidation in the range 0.10 to 0.25 μm. NPG based catalyst on glassy carbon (GC).-Nanoporous Au (NPG) is a nano-material with three dimensional (3D) continuous structure featuring Au with interconnected nano-sized pores and ligaments.1 NPG and other nanoporous metals have been intensively investigated in recent years. This conductive material has an open, 3D porous framework with surface areas that even in an ultrathin NPG layer configuration could be an order of magnitude larger than the area of planar Au. Besides its continuous crystal lattice throughout the porous network, it has a pore size that is adjustable via simple thermal post-processing, which makes it potentially applicable in various fields such as electro-and gas-phase catalysis, optics, sensors and actuators. [2][3][4][5] It is known that nanoparticulate gold possesses remarkable catalytic activity toward oxidation reactions, should the particles be well supported and smaller than 5 nmin size. 6 Recently, ultrathin films of NPG have been shown to serve as catalysts for fuel cell applications as an alternative to their nanoparticle (NP) counterparts.7-9 These films are generated electrochemically under precise potential/current control, which minimizes material loss and surface contamination over the multi-step NP synthetic routines. 7,10 Compared to nanoparticle synthesis which often lacks control due to the large number of the processing steps, ultra thin films of NPG are cost effective, simple to fabricate, and show better reproducibility in terms of quality and reactivity. Another advantage of NPG films is that the edge effect that lowers the catalytic activity characteristic for NP based catalysts does not exist in NPG films due to its continuous nature. 11In our previous work, we established an all-electrochemical synthetic method for a NPG-based catalyst that maximized t...

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Platinum Nanofilm Formation by EC-ALE via Redox Replacement of UPD Copper: Studies Using in-Situ Scanning Tunneling Microscopy

Cited by 145 publications

References 42 publications

Polarization-dependent Total Reflection Fluorescence X-ray Absorption Fine Structure (PTRF-XAFS) Studies on the Structure of a Pt Monolayer on Au(111) Prepared by the Surface-limited Redox Replacement Reaction

Polarization-dependent Total Reflection Fluorescence X-ray Absorption Fine Structure (PTRF-XAFS) Studies on the Structure of a Pt Monolayer on Au(111) Prepared by the Surface-limited Redox Replacement Reaction

Multilayered Nanoclusters of Platinum and Gold: Insights on Electrodeposition Pathways, Electrocatalysis, Surface and Bulk Compositional Properties

Enhanced Adhesion of Ultrathin Nanoporous Au Deposits by Electrochemical Oxidation of Glassy Carbon

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