Underpotential Deposition on Single-Crystal Metals

Small lattice mismatches and gas-phase deposition are typically used for growing epitaxial films on single-crystal substrates. A 1-µm thick film of PbS can be epitaxially electrodeposited onto a Au (100) single crystal. The large lattice mismatch (45.5 %) between Au and PbS is accommodated by the formation of a coincidence lattice, in which the epitaxial film is rotated by 45 degrees relative to the substrate. The coincidence lattice reduces the mismatch to +2.9 %.

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“…The deposition solution was prepared by adding 1m aqueous Na 2 S 2 O 3 3 . The final pH of the solution was adjusted to pH 4.0 with 0.5 m HNO 3 .…”

Section: Methodsmentioning

confidence: 99%

“…Several methods have been used to achieve epitaxial growth from solutions, including chemical bath deposition, [2] underpotential electrodeposition, [3] and electrochemical atomic layer epitaxy. [4] Epitaxial quantum dots of Cd(Se,Te) have been electrodeposited on evaporated Au (111) films.…”

mentioning

confidence: 99%

Epitaxial Electrodeposition of Lead Sulfide on (100)-Oriented Single-Crystal Gold

Vertegel

Shumsky

Switzer

1999

Angew. Chem. Int. Ed.

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“…More recently, Adzic and coworkers applied this concept in making novel Pt monolayer catalysts for the cathode ORR, which is the focus of the review in this section. In general, their method of synthesizing Pt monolayer catalysts involves underpotential deposition (UPD), a technique well known to produce an ordered atomic monolayer metal deposition onto a foreign metal substrate [58][59][60]. Specifically, the method consists of two steps [61,62]: First, a monolayer of a sacrificial less-noble metal is deposited on a more noble metal substrate by UPD, such as Cu UPD on Au or Pd; second, the sacrificial metal is spontaneously and irreversibly oxidized and dissolved by a noble metal cation, such as a Pt cation, which is simultaneously reduced and deposited onto the foreign metal substrate.…”

Section: Orr On Pt Monolayer Electrocatalystsmentioning

confidence: 99%

Recent advances in cathode electrocatalysts for PEM fuel cells

Zhang

2011

Front. Energy

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Great progress has been made in the past two decades in the development of the electrocatalysts for proton exchange membrane fuel cells (PEMFCs). This review article is focused on recent advances made in the kinetic-activity improvement on platinum-(Pt-) based cathode electrocatalysts for the oxygen reduction reaction (ORR). The origin of the limited ORR activity of Pt catalysts is discussed, followed by a review on the development of Pt alloy catalysts, Pt monolayer catalysts, and shape-and facet-controlled Pt-alloy nanocrystal catalysts. Mechanistic understanding is reviewed as well on the factors contributing to the enhanced ORR activity of these catalysts. Finally, future directions for PEMFC catalyst research are proposed.

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“…This implies that the depositing ad-atoms are more strongly to the foreign metal electrode [210][211][212][213]. This implies that the depositing ad-atoms are more strongly to the foreign metal electrode [210][211][212][213].…”

Section: Underpotential Deposition (Upd)mentioning

confidence: 99%

Electrocatalyst Characterization and Activity Validation – Fundamentals and Methods

Sarma

Taufany

2009

Electrocatalysis of Direct Methanol Fuel Cells

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Low-temperature solid polymer electrolyte fuel cells such as direct methanol fuel cells (DMFCs) are gaining more and more attention from both scientific and technological perspectives due to their promising applications for fuel cell vehicles, stationary applications, and portable power sources [1,2]. DMFC simplify the fuel cell system by operating without any external bulky fuel-reforming system and therefore would result in its rapid commercialization. Despite the significant progress, DMFCs still suffer from many obstacles such as low power density, which has been attributed to the poor kinetics of both anode [3], and cathode [4], high flux of water/methanol across membranes [5], and mixed potential at cathode [6]. These phenomena lead to high overpotentials at both the anode and the cathode and, hence, reduction in cell voltage. Other important constraints are the high cost of noble metal catalysts and perfluorosulfonic membranes and higher production costs of the various components of the device.During the past two decades many significant research efforts have been made worldwide on the development of electrocatalyst materials, proton exchange membranes, and modeling and design of cell components and complete stacks for DMFC [7][8][9], and the performance achieved for the state-of-the-art membrane and electrode assemblies in DMFCs can compete favorably with hydrogen-fueled and on-board reforming fuel cell systems [10,11]. Platinum is the best material for the adsorption and dehydrogenation of methanol but, unfortunately, formation of intermediate species such as CO [12], formic acid and formaldehyde poison the platinum anode and impede the catalytic performance for methanol oxidation. The alloying of Pt with promoter metals such as Ru [13][14][15][16][17], Sn [18-22], Mo [23-25], W [26, 27], and Os [28, 29] has been explored as a promising route to minimize the effect of poisonous intermediates. The superior catalytic efficiency of bimetallic Pt-M alloys was explained by the so-called bifunctional mechanism [13, 14, 30-32] and the ligand (electronic) mechanism [17, 33-35]. In the bifunctional mechanism the Electrocatalysis of Direct Methanol Fuel Cells. Edited j115 3.2 Direct Methanol Fuel Cells -Role of Electrocatalysts j117 reducing to water as (ORR): 3=2O 2 þ 6H þ þ 6e À ! 3H 2 O ½E c ¼ 1:23 V vs: SHE ð 3:2Þ Reactions (3.1) and (3.2) can be combined to give the overall reaction (Equation 3.3):The free energy (DG) of overall reaction at 25 C and 1 atm is À686 kJ mol À1 (for CH 3 OH) [59]. Role of Anode Electrocatalysts -Methanol Oxidation Reaction (MOR)The oxidation of methanol and water molecules is the principle reaction occurring at the anode of DMFCs. Pt is the best material for the adsorption and dehydrogenation of methanol. However, formation of intermediate species such as CO [12], formic acid and formaldehyde poison the platinum anode and impede the catalytic performance for methanol oxidation. Among them poisoning from CO species is severe on a Pt electrode surface during the electro-oxidation of...

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Underpotential Deposition on Single-Crystal Metals

Cited by 23 publications

References 175 publications

Epitaxial Electrodeposition of Lead Sulfide on (100)-Oriented Single-Crystal Gold

Epitaxial Electrodeposition of Lead Sulfide on (100)-Oriented Single-Crystal Gold

Recent advances in cathode electrocatalysts for PEM fuel cells

Electrocatalyst Characterization and Activity Validation – Fundamentals and Methods

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