Pt Deposition on Ru Nanoparticles

The concept of a Pt monolayer catalyst was first verified with a Pt submonolayer on Ru substrate. This approach radically changed the design of the Pt-Ru catalysts and it is likely to similarly affect a broad range of catalysts. It facilitates an ultimate reduction of Pt loadings in Pt-Ru catalysts by depositing Pt only at the surface of Ru nanoparticles, so that the most of the Pt atoms become available for the catalytic reaction. Ru (10%) nanoparticles on Vulcan XC-72 carbon were heated in an H2 atmosphere at 3()0°C for 2 h. This temperature is much lower than that required for bulk Ru 

Copyright (2003) with permission from Elsevier, (b) In situ XANES spectra at the Pt L3 of the PtRibo electrocatalyst held at 0.40 V in 1 M HCIO4 electrolyte solution. The spectra were obtained in a fluorescence mode. The spectra of the Pt foil used as a reference and in the calculation of the c/-band vacancies Insert in (b) shows a cubo-octahedral particle model for the electrocatalyst consisting of the Ru particle with two-dimensional Pt islands on its surface. Reprinted from Copyright (2004) with permission from Elsevier. 

A prevailing view of carbon-supported metal nanoparticles is that they are in a form of cubo-octahedral or icosohedral structures.One such model for the active electrocatalyst with submonolayer Pt coverage, a cubo-octahedral Ru particle with Pt islands on its surface, is shown as an inset in Fig. 18b. Pt atoms are in 2D islands as expected from EXAFS measurements and the Ru nanoparticles are supported on a high surface area Vulcan XC-72 carbon. 

In addition to having a good CO tolerance, Pt-Ru electrocatalysts must also have a high activity for H2 oxidation. Comparison of the mass-specific activity of a PtRu2o electrocatalyst with a commercial Pt-Ru 1 1 alloy electrocatalyst for the oxidation of pure H2 showed that its activity is tluee times that of the commercial alloy. This indicates that even for a low Pt coverage on Ru, its activity for H2 oxidation is preserved, a prerequisite for an active CO tolerant catalyst. Comparing the CO tolerance of the PtRu2o electrocatalyst with that of two commercial Pt-Ru alloy electrocatalysts for the oxidation of 1095 ppm CO in H2 confirmed the exceptional stability of the former (Fig. 20) the measurements 

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Wang JX, Brankovic SR, Zhu Y, Hanson JC, Adzic RR (2003) Kinetic characterization of PtRu fuel cell anode catalysts made by sprmtaneous Pt deposition on Ru nanoparticles. 

Fuel cell electrocatalysis also has advanced significantly with innovations in the preparation of active Pt-Ru catalysts. A new type of electrocatalyst was developed, consisting of a Pt submonolayer on Ru nanoparticles. It has high CO tolerance and a very low Pt content. Its synthesis was facilitated by the discovery of electroless deposition of Pt on Ru nanoparticles that can be controlled so that most (> 90%) Pt atoms become available for the catalytic reaction. The catalytic activity of PtRu2o prepared by this method affords considerable advantages in the oxidation of H2, CO, and CH3OH compared with commercial Pt-Ru alloys. 

Synthesize electrocatalysts having a submonolayer Pt loading on Ru nanoparticles by spontaneous deposition of Pt on a Ru surface. 

Electrocatalysts with a 1/8 of monolayer Pt loading on Ru nanoparticles have been synthesized by spontaneous deposition of Pt on a Ru surface, each of which have at least three times larger mass-specific activity for H2 oxidation than two commercial catalysts and a larger CO tolerance, as determined by thin film rotating disk electrode measurements. 

A new method based on spontaneous deposition of Pt on Ru has recently been demonstrated for Pt [340] and Pd [341] deposition on a Ru(OOOl) single crystal surface, which involves a reduction of H2PtCl6 coupled with the oxide formation on Ru [340]. A selective Pt deposition on Ru (no deposition on carbon) is attainable without the application of an external potential [342], Spontaneous deposition of Pt on Ru nanoparticles can be used to control the Pt cluster size and to tune the electronic and catalytic properties of PtRu catalysts. In addition, this approach facilitates a considerable reduction of Pt loadings by depositing Pt at the surfaee of Ru nanoparticles rather than having Pt throughout the PtRu... 

Adzic and coworkers proposed a radically new approach in electrocatalysis and catalysis that can alleviate both problems. It is based on a catalyst consisting of only a submonolayer Pt deposited on carbon-supported Ru nanoparticles. The Pt submonolayer on Ru (PtRu2o) electrocatalyst demonstrated higher CO tolerance than commercial catalysts in rotating disk experiments. Tests of the long-term stabihty of the fuel cells detected no loss in perform-... 

Characterize Pt/Ru electrocatalysts prepared by a new method involving a spontaneous deposition of Pt on Ru nanoparticles. 

In June 2001 we initiated this project to explore the possibilities of decreasing the Pt loading in Pt-Ru catalysts for H2/CO oxidation in the polymer electrolyte membrane fuel cells (PEMFCs). We have demonstrated a new method for the preparation of the Pt-Ru catalysts involving spontaneous deposition of Pt on Ru nanoparticles that we explored first with single crystal Ru surfaces. The resulting catalysts have a high CO tolerance with considerably lower Pt loading than the commercial catalysts. 

Many noble metal nanoparticles (with Ru, Au, Pd, Pt, Os, Ag, Ir, Rh) have been deposited on CNTs and their catalytic activity towards a set of different reactions explored, showing the benefit of the presence of the graphitic support for catalysis. 

Carbon-supported platinum (Pt) and platinum-rathenium (Pt-Ru) alloy are one of the most popular electrocatalysts in polymer electrolyte fuel cells (PEFC). Pt supported on electrically conducting carbons, preferably carbon black, is being increasingly used as an electrocatalyst in fuel cell applications (Parker et al., 2004). Carbon-supported Pt could be prepared at loadings as high as 70 wt.% without a noticeable increase of particle size. Unsupported and carbon-supported nanoparticle Pt-Ru, ,t m catalysts prepared using the surface reductive deposition... 

The catalytic properties of Pt and Ru particles on T102-CNT catalysts in the methanol electro-oxidation were investigated by He et Pt and Ru nanoparticles, approximately of 3 nm in diameter, were uniformly electro-deposited on the as synthesized Ti02-supported C nanotubes. An enhanced and stable catalytic activity was obtained in the electro-oxidation of methanol due to the uniformly dispersed Pt and Ru nanoparticles on the... 

Che et al. also prepared Pt/Ru nanoparticle-filled carbon tubes with a diameter of 200 nm (40). They impregnated carbon-deposited film with a mixture of aqueous solutions of HiPtClf, and RuCI3. After drying in air, the metal compounds in the pores were reduced by H2 flowing at 580°C for 3 h. Then the underlying alumina was dissolved away in HF solution. TEM observation of this sample revealed the presence of Pt/Ru nanoparticles (about 1.6 nm) dispersed on the inner wall of the tubes. 

A series of MSFTIR spectra of CO adsorbed on nm-Pt/GC and Ru-modified nm-Pt/GC electrodes are illustrated in Figure 17(b) [48]. The AIREs are manifested in all spectra. We observe two COl bands from spectra c, d, and e one is the COL-Pt band near 2065 cm and another is the COl-Ru band close to 2025 cm The COl-Ru band appeared as a shoulder peak in spectrum b. It can be seen that the intensity of the COL-Pt band progressively decreases and the intensity of the COl-Ru band increases with the increase of the quantity of Ru deposited on the nm-Pt/GC surface. Nevertheless, the COl-Ru band remains discernible in spectrum e for 10 Ru deposition potential cycles, which may indicate that the nm-Pt/GC surface is still partially covered by Ru. The results imply that the deposition of Ru on an nm-Pt/ GC surface is less efficient than the inverse process, i.e., the deposition of Pt on an nm-Ru/GC surface. Similar results have been reported concerning in-situ FTIRS studies of CO adsorption on Ru ad-atom or Ru nanoparticle modified Pt(lll) single-crystal electrodes [76-78], in which a COL-Pt band near 2070 cm and a COl-Ru band around 2010 cm were observed in the spectra. 

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