Core shell catalysts

Apart from the above described core-shell catalysts, it is also possible to coat active phases other than zeolite crystals, like metal nanoparticles, as demonstrated by van der Puil et al. [46]. More examples of applications on the micro level are given in Section 10.5, where microreactors and sensor apphcations are discussed. 

Cargnello, M., et al., Multiwalled carbon nanotubes drive the activity of metal oxide core-shell catalysts in modular nanocomposites. Journal of the American Chemical Society, 2012. 134(28) p. 11760-11766. 

The 10% Ft ML core-shell catalysts were tested in an MEA and gave satisfactory performance with 10 ppm CO in H2 with an electrode loading of 0.018 mg Ft cm-. i A similar surface modification of a Ft core with Ru has been investigated by Crabb et al. They reported that, on reduction, a surface FtRu alloy formed and showed similar CO tolerance to a conventional nanoparticle FtRu alloy. 

Nanowire-Based Three-Dimensional Hierarchical Core/Shell Catalyst Layer... 

Figure 6.21. Schematics of currently pursued Pt-based electrocatalyst concepts for the ORR. (A) Pt bulk alloys (B) Pt alloy monolayer catalyst concepts (C) Pt skin catalyst concept (D) De-alloyed Pt core-shell catalyst concept.

In this work we present hyperbranched polymers as platforms for catalysts that fall into three major classes, according to their topology and binding mode to the polymeric support (Fig. 2) (i) defined multiple site catalysts (ii) dendritic core-shell catalysts (iii) supramolecular catalyst complexes. 

Figure 3.3.14 displays the results of voltammetric ORR activity measurements of a dealloyed Pt-Cu and a dealloyed Pt-Ni core-shell catalyst under fuel cell relevant conditions. The typical sigmoidal current density electrode potential (i-E) shape (compare to Figure 3.3.10B) of the Pt-based catalyst is clearly evident. The large... 

Figure 3.3.14 Experimental ORR activity of dealloyed Pt-Cu and Pt-Ni core-shell nanoparticle ORR catalysts compared to a pure-Pt nanoparticle catalyst. All three catalyst particles are supported on a high surface area carbon material indicated by the suffix 1C. The shift of the j-E curve of the core-shell catalysts indicates the onset of oxygen reduction catalysis at a more anodic electrode potential (equivalent to a lower overpotential) and hence represents improved ORR reactivity compared to pure Pt.

To inspect and compare the activation overvoltage of the three catalysts in more detail, so-called Tafel plots are used, which plot the cell voltage as a function of the logarithm of the current density. Figure 3.3.16B shows the Tafel plots derived from Figure 3.3.15A. At a cell voltage of 0.9 V, where the overall reaction rate is limited by the chemical surface catalysis, the dealloyed core-shell catalysts perform three... 

In the present study, a comparative investigation of the effects of water on methane oxidation over and core-shell catalysts have been reported. 

Figure 3.4 Schematics of ORR electrocatalyst s morphologies. (A) Metal catalyst such as Pt and metal alloy catalyst such as PtPd supported on a conductive material such as carbon or metal oxide (B) core—shell catalyst such as Au Pt supported on conductive material such as carbon or metal oxide (C) metal catalyst such as Pt and metal alloy catalyst such as PtPd supported on a nanofibre such as carbon or metal-oxide nanofibre and (D) core—shell catalyst such as Au Pt supported on conductive nanotubings such as carbon nanotubings. (For color version of this figure, the reader is referred to the online version of this book.)...

Zhang L, Kim J, Zhang J, Nan F, Gauquelin N, Botton GA, et al. Ti407 supported Ru Pt core—shell catalyst for CO-tolerance in PEM fuel cell hydrogen oxidation reaction. Appl Energy 2013 103(0) 507-13. 

Hsu IJ, Kimmel YC, Jiang XJ, Willis BG, Chen JG (2012) Atomic layer deposition synthesis of platinum-tungsten carbide core-shell catalysts for the hydrogen evolution reaction. Chem Commun 48 1063-1065... 

Dealloyed Pt-Based Core-Shell Catalysts for Oxygen Reduction... 

Abstract In this chapter, we review recent works of dealloyed Pt core-shell catalysts, which are synthesized by selective removal of transition metals from a transition-metal-rich Pt alloys (e.g., PtMs). The resulted dealloyed Pt catalysts represent very active materials for the oxygen reduction reaction (ORR) catalysis in terms of noble-metal-mass-normalized activity as well as their intrinsic area-specific activity. The mechanistic origin of the catalytic activity enhancement and the stability of dealloyed Pt catalysts are also discussed. 

Core-Shell Catalysts in PEMFC Cathode Environments... 

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. 

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