Preparation of Carbon-Supported Electrocatalysts

This indicates that cos GhjO increases with the increase in oxygen content and decreases with the decrease in hydrogen content. This relationship was confirmed by the results of Kinoshita et al. [94] on the electrochemical treatment of carbon blacks. Hydrophilic carbons provide high catalyst utilization factors, whereas hydrophobic carbons (or graphitized carbons) allow easy water removal, avoid flooding of the CLs, and ensure better resistance to corrosion [8,96,97]. 

CARBON MATERIALS AS SUPPORTS FOR FUEL CELL ELECTROCATALYSTS 

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The right choice of a carbon support greatly affects cell performance and durability. The purpose of this chapter is to analyze how structure and properties of carbon materials influence the performance of supported noble metal catalysts in the CLs of the PEMFCs. The review chapter is organized as follows. In Section 12.2 we give an overview of carbon materials utilized for the preparation of the catalytic layers of PEMFC. We describe traditional as well as novel carbon materials, in particular carbon nanotubes and nanofibers and mesoporous carbons. In Section 12.3 we analyze properties of carbon materials essential for fuel cell performance and how these are related to the structural and substructural characteristics of carbon materials. Sections 12.4 and 12.5 are devoted to the preparation and characterization of carbon-supported electrocatalysts and CLs. In Section 12.6 we analyze how carbon supports may influence fuel cell performance. Section 12.7 is devoted to the corrosion and stability of carbon materials and carbon-supported catalysts. In Section 12.8 we provide conclusions and an outlook. Due to obvious space constraints, it was not possible to give a comprehensive treatment of all published data, so rather, we present a selective review and provide references as to where an interested reader may find more detailed information. 

Li X, Huang Q, Zou Z, Xia B, Yang H (2008) Low temperature preparation of carbon-supported Pd Co alloy electrocatalysts fm methanol-tolerant oxygen reduction reaction. Electrochim Acta 53 6662-6667... 

Rojas S, Garcia-Garcia FJ, Jaras S, Martinez-Huerta MV, Fierro JLG, Boutonnet M. Preparation of carbon supported Pt and PtRu nanoparticles from microemulsion electrocatalysts for fuel cell applications. Appl Catal A 2005 285 24-35. 

PtRu is the effective electrocatalyst for methanol oxidation reaction and the dispersion of the metal particles is of great importance for the utilization and activity, so we also compare several methods for the preparation of carbon-supported PtRu catalyst Similar to the reasons mentioned in Section 10.2.1 for Pt/C, high metal loadings are required for the PtRu/C catalyst We use 20wt Pt% —lOwt % Ru/C as an... 

Heteronuclear Pt-Ru binary carbonyl clusters have been used for the preparation of tailored PtRu bimetallic electrocatalysts. The use of carbonyl complexes such as Ru4Pt2(CO)i8 and closely related carbide and hydride carbonyl-derived clusters, that is, Ru5PtC(CO)i6 and Ru6Pt3(CO)2i( X3-H)( x-H)3, has allowed the preparation of carbon- and y-Al203-supported catalysts in which the presence of RugPts, RusPt and Ru4Pt2 clusters or nanoparticles has been reported [62-65]. 

As well, EXAFS has been used to confirm that several series of carbon supported PtCo catalysts prepared by SEA are completely alloyed. The development of these alloys for fiael cell electrocatalysts, along with carbon supported Pt/Mo and Pt/Ru, is presently under way. 

In another work, Shukla and co-authors [27] studied the electrocatalytic activity of carbon-supported Pt-Au alloy catalysts, with different atomic ratios, to improve the oxygen reduction reaction (ORR) kinetics and methanol tolerance, in a direct methanol fuel ceU. The electrocatalysts were prepared by codeposition of Pt and Au nanoparticles onto a carbon support. 

Herrmann I, Briiser V, Fiechter S, Kersten H, Bogdanoff P (2005) Electrocatalysts for oxygen reduction prepared by plasma treatment of carbon-supported cobalt tetramethoxy-phenylporphyrin. J Electrochem Soc 152 A2179-A2185... 

Chien CC, Jeng KT. Effective preparation of carbon nanotube-supported Pt-Ru electrocatalysts. Mater Chem Phys 2006 99 80-7. 

Maillard F, Gloaguen F, Leger JM. Preparation of methanol oxidation electrocatalysts ruthenium deposition on carbon-supported platinum nanoparticles. J Appl Electrochem 2003 33 1-8. 

Attwood PA, McNicol BD, Short RA. The electrocataljdic oxidation of methanol in acid electrolyte preparation and characterization of noble metal electrocatalysts supported on pre-treated carbon-fibre papers. J Appl Electrochem 1980 10 213-22. Frelink T, Visscher W, Van Veen JAR. Particle size effect of carbon supported platinum catalysts for the electrooxidation of methanol. J Electroanal Chem 1995 382 65-72. 

J. Luo,N. Kariuki, L. Han, L. Wang, C. -J. Zhong etal., Preparation and characterization of carbon-supported PtVFe electrocatalysts , Electrochim. Acta 51 (2006) 4821. 

G. Zehl, I. Dorbandt, S. Fiechter, P. Bogdanofif, On the influence of preparation parameters on the catalytic properties of carbon supported Ru-Se electrocatalysts , J. New Mat. Electrochem. Systems, accepted. 

Au in Pt (ca. 4%) being relatively low at ambient temperature. However, homogeneous alloys of these two metals can be produced if the particle size is quite small and such alloys often have superior catalytic activity [74], The preparation and analysis of a range of Au/Pt alloy nanoparticle electrocatalysts and their use for oxygen reduction in both acid and base have also been described [75,76], In addition, Adzic et al. [77] demonstrated that the stability, with respect to dissolution, of carbon-supported Pt electrocatalysts for oxygen reduction in acid solution was increased by depositing some Au clusters on the Pt nanoparticles it was suggested that the presence of the Au raises the oxidation potential of the Pt. 

Recently, rhodium and ruthenium-based carbon-supported sulfide electrocatalysts were synthesized by different established methods and evaluated as ODP cathodic catalysts in a chlorine-saturated hydrochloric acid environment with respect to both economic and industrial considerations [46]. In particular, patented E-TEK methods as well as a non-aqueous method were used to produce binary RhjcSy and Ru Sy in addition, some of the more popular Mo, Co, Rh, and Redoped RuxSy catalysts for acid electrolyte fuel cell ORR applications were also prepared. The roles of both crystallinity and morphology of the electrocatalysts were investigated. Their activity for ORR was compared to state-of-the-art Pt/C and Rh/C systems. The Rh Sy/C, CojcRuyS /C, and Ru Sy/C materials synthesized by the E-TEK methods exhibited appreciable stability and activity for ORR under these conditions. The Ru-based materials showed good depolarizing behavior. Considering that ruthenium is about seven times less expensive than rhodium, these Ru-based electrocatalysts may prove to be a viable low-cost alternative to Rh Sy systems for the ODC HCl electrolysis industry. 

Similarly, Pd, Ag, and Pd-Ag nanoclusters on alumina have been prepared by the polyol method [230]. Dend-rimer encapsulated metal nanoclusters can be obtained by the thermal degradation of the organic dendrimers [368]. If salts of different metals are reduced one after the other in the presence of a support, core-shell type metallic particles are produced. In this case the presence of the support is vital for the success of the preparation. For example, the stepwise reduction of Cu and Pt salts in the presence of a conductive carbon support (Vulcan XC 72) generates copper nanoparticles (6-8 nm) that are coated with smaller particles of Pt (1-2 nm). This system has been found to be a powerful electrocatalyst which exhibits improved CO tolerance combined with high electrocatalytic efficiency. For details see Section 3.7 [53,369]. 

M. Morita, Y. Iwanaga, and Y. Matsuda, Anodic-oxidation of methanol at a gold-modified platinum electrocatalyst prepared by RE-sputtering on a glassy-carbon support, Electrichim. Acta 36, 947-951 (1991). 

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