Electrodeposition electrocatalyst

Reactions in which the nature of the substrate is vital (e.g., as in electrocatalysis, corrosion, electrodeposition) do not offer opportunities for application of a technique in which the substrate is regarded essentially as an electron source or sink, rather than as an electrocatalyst. The very large field of bioelectrochemistiy (which involves concepts such as enzymes as electrodes and even offers electrochemical mechanisms for metabolism) would offer difficulties for potential sweep applications because of the very high resistance of the substrate.21... 

Three techniques have been described in the literature to prepare combinatorial libraries of fuel cell electrocatalysts solution-based methods [8, 10-14], electrodeposition methods [15-17] and thin film, vacuum deposition methods [18-21]. Vacuum deposition methods were chosen herein for electrocatalyst libraries in order to focus on the intrinsic activity of the materials, e.g., for ordered or disordered single-phase, metal alloys. 

Model electrodes with a dehned mesoscopic structure can be generated by a variety of means, e.g., electrodeposition, adsorption from colloidal solutions, and vapor deposition and on a variety of substrates. Such electrodes have relatively well-dehned physico-chemical properties that differ signihcantly from those of the bulk phase. The present work analyzes the application of in-situ STM (scanning tunneling microscopy) and ETIR (Eourier Transformed infrared) spectroscopy in determining the mesoscopic structural properties of these electrodes and the potential effect of these properties on the reactivity of the fuel cell model catalysts. Special attention is paid to the structure and catalytic behavior of supported metal clusters, which are seen as model systems for technical electrocatalysts. 

Since on pure platinum, methanol oxidation is strongly inhibited by poison formation, bimetallic catalysts such as PtRu or PtSn, which partially overcome this problem, have received renewed attention as interesting electrocatalysts for low-temperature fuel cell applications, and consequently much research into the structure, composition, and mechanism of their catalytic activity is now being undertaken at both a fundamental and applied level [62,77]. Presently, binary PtRu catalysts for methanol oxidation are researched in diverse forms PtRu alloys [55,63,95], Ru electrodeposits on Pt [96,97], PtRu codeposits [62,98], and Ru adsorbed on Pt [99]. The emphasis has recently been placed on producing high-activity surfaces made of platinum/ruthenium composites as a catalyst for methanol oxidation [100]. 

Different electron-conducting polymers (polyaniline, polypyrrole, polythiophene) are considered as convenient substrates for the electrodeposition of highly dispersed metal electrocatalysts. The preparation and the characterization of electronconducting polymers modified by noble metal nanoparticles are first discussed. Then, their catalytic activities are presented for many important electrochemical reactions related to fuel cells oxygen reduction, hydrogen oxidation, oxidation of Cl molecules (formic acid, formaldehyde, methanol, carbon monoxide), and electrooxidation of alcohols and polyols. 

Taylor et al.8 were the first to report an electrochemical method for preparation of MEAs for PEMFCs. In their technique, Pt was electrochemically reduced and deposited at the electrode membrane interface, where it was actually utilized as an electrocatalyst. Nation, which is an ion exchange polymer membrane, is first coated on a noncatalyzed carbon support. The Nafion-coated carbon support is then immersed into a commercial acidic Pt plating solution for electrodeposition. Application of a cathodic potential results in diffusion of platinum cations through the active Nation layer. The migrated platinum species are reduced and form Pt particle at the electrode/membrane interface only on the sites which are both electronically and ionically conductive. The deposition of Pt particles merely at the electrode/membrane interface maximizes the Pt utilization. The Pt particles of 2-3.5 nm and a Pt loading of less than 0.05 mg cm-2 were obtained employing this technique.8 The limitation of this method is the difficulty of the diffusion of platinum... 

In practice, deposits with high roughness factor and good mechanical resistance are of particular interest. Dendrites have low mechanical resistance and they are unsuitable as electrocatalysts, but the elucidation of the Ohmic-controlled electrodeposition of metals due to the dendritic growth is of a great theoretical importance. 

In Chapter 4 by Popov et al., the aspects of the newest developments of the effect of surface morphology of activated electrodes on their electrochemical properties are discussed. These electrodes, consisting of conducting, inert support which is coated with a thin layer of electrocatalyst, have applications in numerous electrochemical processes such as fuel cells, industrial electrolysis, etc. The inert electrodes are activated with electrodeposited metals of different surface morphologies, for example, dendritic, spongy-like, honeycomblike, pyramid-like, cauliflower-like, etc. Importantly, the authors correlate further the quantity of a catalyst and its electrochemical behavior with the size and density of hemispherical active grain. 

From the electrochemical engineering point of view, the electrocatalyst design depends on the purpose of the electrochemical reactor, gas electrosynthesis, organic synthesis, batteries or supercapacitors, metal electrodeposition, and the fuel cells. 

Pd nanoparticles supported on PANI-NFs are efficient semi-heterogeneous catalysts for Suzuki coupling between aryl chlorides and phenylboronic acid, the homocoupling of deactivated aryl chlorides, and for phenol formation from aryl halides and potassium hydroxide in water and air [493], PANl-NF-supported FeCl3 as an efficient and reusable heterogeneous catalyst for the acylation of alcohols and amines with acetic acid has been presented [494]. Vanadate-doped PANI-NFs and PANI-NTs have proven to be excellent catalysts for selective oxidation of arylalkylsulfides to sulfoxides under nuld conditions [412]. Heterogeneous Mo catalysts for the efficient epoxidation of olefins with ferf-butylhydroperoxide were successfully synthesized using sea urchin-Uke PANI hollow microspheres, constructed with oriented PANI-NF arrays, as support [495]. Pt- and Ru-based electrocatalyst PANI-NFs—PSSA—Ru—Pt, synthesized by the electrodeposition of Pt and Ru particles into the nanofibrous network of PANI-PSSA, exhibited an excellent electrocatalytic performance for methanol oxidation [496]. A Pt electrode modified by PANI-NFs made the electrocatalytic oxidation reaction of methanol more complete [497]. Synthesis of a nanoelectrocatalyst based on PANI-NF-supported... 

Electrodeposition. In this process, a conductive substrate is placed in an electrolyte solution (typically aqueous) that contains a salt of the material of interest. When an electrical potential is apphed between the substrate and a counter electrode, redox chemistry takes place at the surface of the substrate which deposits material. Complex pulse trains and/or high-pulse frequencies are sometimes used to direct current flow and favor desired reactions. A postsynthesis calcination is often performed to reach a desired material phase. Electrodeposition is restricted to deposition of electrically conductive materials and produces polycrystaUine and amorphous films. This process is also appropriate for thin film surface treatment of PEC electrodes, such as electrocatalyst deposition. 

Gasparotto LHS, Ciapina EG, Ticianelli EA, Tremiliosi-Filho G (2012) Electrodeposition of PVA-protected PtCo electrocatalysts for the oxygen reduction reaction in H2SO4. J Power Sources 197 97-101... 

Reports on the use of monomeric or polymeric porphyrins as electrocatalysts for the detection of phenols are limited. Chen and Chen reported on the use of FeTMPyP in solution, in the presence of DNA or electrodeposited on a GCE previously modified with DNA, for the catalysis of the reduction of p-nitrophenol. ... 

Current synthetic methods for the preparation of Pd-based electrocatalysts for anodes of DAFCs are manifold, including reduction of high-valent metal compounds with chemical agents, colloidal metal deposition, electrodeposition and transmetalation... 

Electrochemical methods for the preparation of anode electrocatalysts for DAFCs involve either the electrodeposition of one metal at a time, eventually followed by the electrodeposition of other metals, or the contemporaneons electrodeposition of two or more metals. Highly ordered Pd nanowires arrays (Fig. 5) have been prepared by template-electrodeposition on glassy carbon electrodes, while cyclic potential sweep techniqnes have been used to prepare Pd thin films on polyciystalline Pt or An substrates. Ni-Pd electrodes for methanol oxidation have been prepared by electrodeposition onto titaninm discs nsing a PdCl2/NiS04-7H20 bath." ... 

Pt-Ru electrocatalysts are generally considered to be the most active binary catalysts for the MOR. Several commercial Pt-Ru alloy nanoparticles supported on carbon black have been available for applications in DAFCs. The catalytic effect has been observed using different kinds of Pt-Ru materials, such as adsorbed Ru on bulk Pt [46, 47], UHV-evaporated Ru on bulk Pt [46, 47], Pt-Ru electrodeposits [48, 49], Pt-Ru alloys [50-60], and Pt-RuOj [63-66]. 

Pt Clg], and Cu, respectively, resulting in the individual metal nanoparticles, the size and morphology, and the relative ratio of the crystalline facets of which are unique and different from those of the corresponding nanoparticles electrodeposited conventionally. Some factors controlling the disproportionations and their mechanisms are also discussed. A disproportionation reaction-driven electroless deposition in RTILs is expected as a promising procedure to develop novel nanostructures such as electrocatalysts. 

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