Core-shell catalysts electrochemical

Core-shell catalyst materials may also be prepared by non-electrochemical routes. Core-shell nanoparticles may be produced in solutimi using colloidal methods, by sequential deposition of the core and shell components [33], or Pt layers may be deposited chemically or via displacement reactions onto preprepared core nanoparticles, but in cmitrast to approaches described in Sect. 19.3.1, no applied potential is required typically core particles or colloidal core-shell particles are deposited onto carbon supports. 

Chapters 18-21 discuss core-shell and advanced Pt alloy catalysts (which also can be considered to have a core-shell structure). Chapter 18 studies the fundamentals of Pt core-shell catalysts synthesized by selective removal of transition metals from transition metal-rich Pt alloys. Chapter 19 outlines the advances of core-shell catalysts synthesized by both electrochemical and chemical methods. The performance, durability, and challenges of core-shell catalyst in fuel cell applications are also discussed. Chapter 20 reviews the recent analyses of the various aspects intrinsic to the core-shell structure including surface segregation, metal dissolution, and catalytic activity, using DFT, molecular dynamics, and kinetic Monte Carlo. Chapter 21 presents the recent understanding of activity dependences on specific sites and local strains in the surface of bulk and core-shell nanoparticle based on DFT calculation results. 

Kulp, C., Chen, X., Puschhof, A., Schwamborn, S., Schuhmann, W., and Bron, M. (2010) Electrochemical synthesis of core-shell catalysts for electrocatalytic applications. ChemPkysChem, 11, 2854 2861. 

Wei ZD et al (2008) Electrochemically synthesized Cu/Pt core-shell catalysts on a porous carbon electrode for polymer electrolyte membrane fuel cells. J Power Sources 180 84—91... 

With all these electrochemical preparation techniques for core-shell catalysts, up-scaling is a critical issue. Typically the above preparations are carried out emplo)dng small substrate electrodes of several mm in diameter. Attempts to scale up electrochemical syntheses of core-shell catalysts, however, have been report consisting in electrochemical dealloying of catalysts in membrane-electrode-assemblies [29] or scale-up of the redox-exchange approach [31]. 

In this chapter, two carbon-supported PtSn catalysts with core-shell nanostructure were designed and prepared to explore the effect of the nanostructure of PtSn nanoparticles on the performance of ethanol electro-oxidation. The physical (XRD, TEM, EDX, XPS) characterization was carried out to clarify the microstructure, the composition, and the chemical environment of nanoparticles. The electrochemical characterization, including cyclic voltammetry, chronoamperometry, of the two PtSn/C catalysts was conducted to characterize the electrochemical activities to ethanol oxidation. Finally, the performances of DEFCs with PtSn/C anode catalysts were tested. The microstmc-ture and composition of PtSn catalysts were correlated with their performance for ethanol electrooxidation. 

Our cubo-octahedral structures were of the core-shell t5rpe with inner core, formed by second component atoms - transition metals, while the shell in just one atomic layer was constructed by platinum - active catalyst of surface processes. Such structures in our own calculations [25] and others [26-27] are optimal in catalytic sense, because they cause effective way of surface reactions for oxygen reduction. On the other side such nanoclusters possess stability in aggressive acid environments, which lead to electrochemical corrosion of materials of catalysts. 

Some non-carbon supports are also electrochemically unstable. For example, when TIC was used as a catalyst support to form Pt/TiC and PtsPd/TiC ORR catalysts, its electrooxidation at potential higher than 0.8 V vs RHE was found. When TiC Ti02 core—shell composite was used for the support, the electrochemical stabilities were significantly improved. 

A series of PfML/Pd/C core-shell samples with varying nominal Pt shell thickness have also been prepared via a proprietary chemical method and explored using X AS and electrochemical techniques [26]. Analysis of EXAFS at the Pd K and ft L3 edges for catalyst pellet samples revealed the expected increase in ft-ft and decrease in Pd-ft and Pt-Pd neighbors with increasing nominal ft coverage from 0.5 to 2 monolayers of ft (calculated based on catalyst surface area of the Pd/C cores). Further EXAFS measurements under electrochemical control in liquid electrolytes revealed an increase in average Pd-Pd bond distance to 2.780 A at 0.0 V for the 0.5 of... 

Electrochemical leaching of Pt alloy catalysts has been deliberately applied to form core-shell materials with enhanced activities, either in half-cell tests [24, 25] or even... 

Abstract One of the most critical fuel cell components is the catalyst layer, where electrochemical reduction and oxidation of the reactants and fuels take place kinetics and transport properties influence cell jjerformance. Fundamentals of fuel cell catalysis are explain, concurrent reaction pathways of the methanol oxidation reaction are discussed and a variety of catalysts for applications in low temperature fuel cells is described. The chapter highlights the most common polymer electrolyte membrane fuel cell (PEMFC) anode and cathode catalysts, core shell particles, de-alloyed structures and platinum-free materials, reducing platinum content while ensuring electrochemical activity, concluding with a description of different catalyst supports. The role of direct methanol fuel cell (DMFC) bi-fimctional catalysts is explained and optimization strategies towards a reduction of the overall platinum content are presented. 

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