Electrochemical dealloying

Selective electrochemical dealloying is an important method for preparing nanoporous metal materials. These processes are strongly dictated by the kinetics and thermodynamic driving forces at the atomic scale, thus providing 

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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. 18.6 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])...

Core-shell structures may also be achieved via annealing of alloy particles under particular atmospheres or dealloying of the more oxidizable elements from alloy nanoparticles. Electrochemical dealloying approaches are generally used to generate a Pt-rich shell and base-metal-rich core and are reviewed in detail in Chap. 18. 

Electrochemical dealloying of ft-Ag [38] and other ft-metal core-shell systems has been used to produce hollow ft spheres. This is a manifestation of the nanoscale Kirkendall effect whereby less stable core metal atoms are lost from the center of... 

Strasser et al. [59, 67, 91-94] recently apphed a freeze-diying technique in the synthesis of ft alloy nanoparticle catalysts with enhanced ORR activity. The ft-Cu alloy catalyst after electrochemical dealloying was reported to have both mass and specific activities about four to six times those of a standard commercial Pl/C catalyst, in both RDE and MEA tests. The synthesis involved an impregnati(Mi/freeze-diying route followed by annealing. Preparation started with impregnation and smiication of... 

Fig. 10.5 (a) The schematic model of a Pt-Cu alloy particle before and after electrochemical dealloying of the near-surface Cu atoms (pink balls = Cu atoms gray balls = Pt atoms) (b) Pt mass activities of Pt-Cu/C catalysts at various annealing temperatures compared to that of Pt/C catalyst (Reproduced from [67]. With permission)... 

FIGURE 4.4 Electrochemical dealloying of Cu rich Pt-Cu alloy resulting in a core-shell structure with a Pt-rich shell. Reprinted with permission from S. Koh, P. Strasser, J. Amer. Chem. Soc., 129 (2007) 12624. Copyright 2007 American Chemical Society. 

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]. 

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