Pt Core-Shell Catalysts

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.

Figure 3.5 TEM imagines for several typical electrocatalysts. (A) PtRu alloy supported on carbon particles (PtRu/C) (B) Pt supported on TiOa nanofibers (Pt/TiOa) ("Ti02-supported Pt electrocatalysts for oxygen reduction reaction", Robert Hui, and Jiujun Zbang, unpublished work) and (C) Tl407-supported Ru Pt core-shell catalyst. (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. 

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. 

Ball S, Burton SL, Fisher J, O Malley R, Tessier B, Theobald BRC, Thompsett D, Zhou WP, Su D, Zhu Y, Adzic RR (2009) Structure and activity of novel Pt-core-shell catalysts for the oxygen reduction reaction. ECS Trans 25(1) 1023-1036... 

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. 

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... 

As discussed previously, the DoE has set a target of catalyst activity of four times fhaf of pure Pt/carbon. This can be expressed as activity per mass of Ft or acfivify per cost equivalent. Three general approaches have been investigated to achieve this target Pt alloys, Pt core-shells, and non-Pt catalysts... 

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.

From combined theoretical and experimental insights, nanostructured Pt core-shell electrocatalyst architectures have recently emerged as promising, cost-effective cathode fuel cell catalysts. Pt-enriched multilayer surface shells surround Pt-poor cores that modify the reactivity of the surface Pt layer. 

It is worthwhile to point out that during the last decade, carbon-supported Au Pt core—shell nanostructured catalysts were explored and synthesized to improve the ORR performance of the electrocatalyst. ° The results showed that the limiting... 

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

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. 

Fig. 19.11 HAADF-STEM and Pt, Ir, and Ni line scans for PtML/IrNi core-shell catalyst before testing (a and c) and after 50,000 cycles (b and d) 0.6-1.0 V at 50 mV/s, RT, 0.1 M HCIO4 electrolyte [29]...

In contrast to Pd and Pt, there is a lower natural abundance of Ir in metal ores [66], so using a substantial amount of Ir within the core of a core-shell catalyst would be likely to increase Ir cost and make such a catalyst inappropriate as a longterm use in automotive PEMFC systems. The effect of Ir content on likely cost of both alloy and core-shell catalysts should therefore be scrutinized as well as the activity per mgPt. 

Kotmigsmaim C, Santnlli AC, Gmig K, Vukmirovic MB, Zhou W-P, Sutter E, Wong SS, Adzic RR (2011) Enhanced electrocatalytic performance of processed, ultrathin supported Pd-Pt core-shell nanowire catalysts fm the oxygen reduction reactiorr J Am Chem Soc 133 9783—9795... 

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