Dealloyed catalyst

It is still tmclear that which kind of core-shell structure contributes the most to the macroscopic overall catalytic activities of the dealloyed catalyst particle ensemble. Researchers at General Motors found that the single-core-shell nanoparticles provided most of the activity for dealloyed PtCus catalyst [3], while Snyder et al. fotmd that nanoporous dealloyed PtNis particles exhibited higher mass activity and specific activity compared to the dealloyed solid nanoparticles PtNi3 with smaller sizes [80]. Further studies are needed to clarify this issue. 

DFT approach is consistently used to resolve electronic structure features of various advanced catalyst concepts including core-shell catalyst, nanostructured shape-selective catalysts, Pt monolayer catalyst, and selectively dealloyed catalysts... 

Work on dealloyed catalysts was supported by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy under grant DE-EE0000458. 

Oxygen reduction mass activities of dealloyed ternary Pt alloy catalysts as cathodes in MEAs at 80°C, 150 kPa Oj. (R. Srivastava et al., Angewandte Chemie International Edition (2007), 46,8988. Copyright Wiley-VCH Verlag GmbH Co. KGaA. Reproduced with permission.)... 

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.

Subsequent deployment of the new catalyst in the cathode layer of small-area MEAs first, then large-area MEAs, and finally fuel cell stacks represents the typical series of performance tests to check the practical viability of novel ORR electrocatalyst materials. Figure 3.3.15A shows the experimental cell voltage current density characteristics (compare to Figure 3.3.7) of three dealloyed Pt-M (M = Cu, Co, Ni) nanoparticle ORR cathode electrocatalysts compared to a state-of-the-art pure-Pt catalyst. At current densities above 0.25 A/cm2, the Co- and Ni-containing cathode catalysts perform comparably to the pure-Pt standard catalyst, even though the amount of noble metal inside the catalysts is lower than that of the pure-Pt catalyst by a factor of two to three. The dealloyed Pt-Cu catalyst is even superior to Pt at reduced metal loading. 

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... 

Strasser P, Koh S, Anniyev T, et al. Lattice-strain control of the activity in dealloyed core -shell fuel cell catalysts. Nat Chem. 2010 2 454-60. 

Therefore, higher surface areas could be provided from catalysts which are amorphous, less uniform, and smaller in feature size. Dealloying could be a novel approach for the preparation of highly porous catalysts bearing these desired properties. Pt and Al were deposited on Teflon and an... 

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. 

Dealloyed Pt-Bimetallic Nanoparticle Catalysts 18.3.1 Dealloyed PtCus Catalysts Synthesis and Activities... 

The synthesis of dealloyed PtCus catalyst involved the preparation of PtCus precursor alloys at the first step, which was followed by electrochemical dissolution of Cu (dealloying). PtCus alloy precursors were prepared by a conventional... 

Fig. 18.4 (a) Initial three CVs of the PtCus catalyst annealed at 600 °C during electrochemical dealloying compared to the CV of a commercial Pt catalyst (reprint with permission from ref [27]). (b) Diagrammatic illustration of how the critical dissolution potential of a Cu monolayer depends on the composition of its subsurface layer (reprint with permission from ref [40])... 

After 200 cycles of electrochemical dealloying, the Cu dissolution vanished completely and the CV for aU the dealloyed PtCua catalysts exhibited stable Pt-like... 

Fig. 18.5 (a) ORR voltammetry in 02-saturated 0.1 M HCIO4 of dealloyed PtCu3 catalysts using the alloy precursors annealed at 600, 800, and 950 compared to a commercial Pt catalyst. (Inset) CV curves of the dealloyed PtCu3 catalysts in N2 saturated 0.1 M HCIO4. (b) Comparison of Pt-mass activities at 0.9 V/RHE. (c) Comparison of Pt-area-specific activities at 0.9 V/RHE (reprint with permission from ref. [27])... 

Fig. 18.6 A novel three-step method for in situ electrochemical dealloying of transition-metal-rich Pt alloy catalyst inside MEA (reprint with permission from ref. [41])...

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