Core-shell catalysts reduction

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. 

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.

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nanofibers (Pt/TiOa) ("Ti02-supported Pt electrocatalysts for oxygen reduction reaction", Robert Hui, and Jiujun Zbang, unpublished work) and (C) Tl407-supported Ru Pt core-shell catalyst.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.)...

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. 

It has been repeatedly observed by various researchers that the very high oxygen reduction activities reported for core-shell catalyst materials measured with the... 

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... 

The electrocatalysts for various catalytic processes contain noble metals. Due to high prices and limited resources of noble metals, reduction of their content in catalysts is needed. Core-shell catalysts offer an attractive choice since noble metals (active component) are restricted to the surface in the shell of a catalyst, while core can be made of less expensive metals. In this way ultimate reduction in noble metal loading and its complete utilization can be achieved, while core-shell interaction can change electronic properties of noble metal shell making it more active and durable. One of the most attractive types of core-shell catalyst is a Pt L electrocatalysts for ORR. 

The two-step synthesis (subsequent reduction of the precursor salts) is more likely to result in phase-separated catalysts, possibly core-shell catalysts. Typically a colloid of a particular metal is first formed then subsequently reacted with the salt of the second metal. Numerous examples of such reactions exist in the literature [95, 96]. The deposition of the seeond metal onto the preformed colloid can be driven by a redox reaction if the seeond metal is more noble than the metal of flic preformed colloid, i.e., depending on the difference in the free energy (AG), which is determined by the difference in the equilibrium potentials, Ei and E2 of the redox reactions of the two metal/salts, as follows [97] ... 

Another interesting feature of these core-shell catalysts is the effect of reduction on the accessibility of reactants to the Pd. 

Maye et al. studied gold nanoparticles supported on carbon black for ORR in both acidic and alkaline media.210 The gold nanoparticles were of a core-shell type where the particle consisted of a gold nanocrystal core of 1-6 nm in diameter that was surrounded by an organic monolayer shell.214 While the Au/C catalyst was found to be active for ORR, its activity was much lower than that of Pt/C, PtRu/C and AuPt/C. The electron transfer in 0.5 M H2S04 was reported as 2.9 0.2, indicating a mixed reduction pathway.210... 

Figure 24. Core and shell mechanism of catalyst reduction [264]...

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