Carbon black supported platinum

The influence of catalyst preparation on the surface properties of fine carbon black-supported platinum particles of similar size (4nm) was investigated. Different adsorption behavior was indicated by varying shapes and fine structures of the vibrational modes of the dissociatively adsorbed atomic hydrogen on these nanoparticles (58b). 

For a carbon black-supported platinum catalyst, the roughness factor can be very high (1 to 10 ), depending on the dispersion of the active components and their microstructure. 

The PAFC is based on an immobilized phosphoric acid electrolyte. The matrix universally used to retain the acid is silicon carbide, and the catalyst for both the anode and cathode is platinum [8], The active layer of platinum catalyst on a carbon-black support and a polymer binder is backed by a carbon paper with 90% porosity, which is reduced to some extent by a Teflon binder [6,9]. 

P. Albers, E. Auer, K. Ruth S.F. Parker (2000). J. CataL, 196, 174-179. Inelastic neutron scattering investigation of the nature of surface sites occupied by hydrogen on highly dispersed platinum on commercial carbon black supports. 

In the present article, the size and the loading efficiency of metal particles were investigated by changing the preparation method of carbon-supported platinum catalysts. First, the effect of acid/base treatment on carbon blacks supports on the preparation and electroactivity of platinum catalysts. Secondly, binary carbon-supported platinum (Pt) nanoparticles were prepared using two types of carbon materials such as carbon blacks (CBs) and graphite nanofibers (GNFs) to check the influence of carbon supports on the electroactivity of catalyst electrodes. Lastly, plasma treatment or oxyfluorination treatment effects of carbon supports on the nano structure as well as the electroactivity of the carbon supported platinum catalysts for DMFCs were studied. 

Munke et al. [196] reported a technique (Figure 10.31) of in situ electrochemical FTIR and used it to study a real carbon-supported platinum + ruthenium catalyst. Different adsorptions were observed when methanol was electrooxidized at bulk Pt, Pt particles, and carbon-black-supported Pt -I- Ru electrodes, particularly with regard to the nature of the adsorbed CO species (Figure 10.32). 

This chapter reviewed various one-dimensional catalyst supports including carbon nanotubes, carbon nanofibers and metal oxide nanowires as replacement of carbon black support to increase the utilization of platinum and enhance the durability of electrodes in fuel cells. 

Carbon black is favorable as a support material not only because of its high surface area and electronic properties, but it is also abundant, chemically inert, and environmental friendly (Bleda-Martinez et al., 2007). Carbon blacks are typically used as supports which are manufactured by the pyrolysis of hydrocarbons or oil fractions using oil furnaces or acetylene processes. Some of the most common carbon blacks used for platinum deposition in PEMFC catalysts are synthesized using the furnace method where the input materials are burned with hmited air at about 1400°C (Dowlapalli et al., 2006). Vulcan XC-72 and Black Pearl 2000 represent these types of carbon blacks. These carbon blacks are easily made and abundant making them popular choices for carbon black supports for Pt/C catalysts (Cameron et al., 1990). 

For the electrooxidation of alcohols in alkaline medium (see Section 6.4), Shen et al. (2006) suggested a platinum or palladium catalyst promoted with 25 wt% of nickel oxide NiO deposited on a carbon-black support. According to then-data, this additive substantially accelerates the electrooxidation of methanol in an alkaline medium. Tarasevich et al. (2005) suggested a Ru-Ni catalyst deposited on carbon black for the electrooxidation of ethanol in an alkaline medium it is considerably more active than pure ruthenium. Under the operating conditions of fuel cells in acidic media as well as in contact with proton-conducting membranes of the Nafion type, the use of nonplatinum catalysts is highly restricted, owing to corrosion problems. 

In this connection it can be noted that Guha et al. (2010) investigated the influence of carbon support morphology on the behavior of a PEMFC membrane electrolyte assembly. Platinum electrocatalyst particles were deposited on lower-surface-area fibrous (carbon nanofibers) and particulate (carbon blacks) supports. The performance was shown to be independent of the carbon support morphology. 

The gas-phase oxidation of carbon blacks by oxygen and/or water is strongly catalyzed by the presence of catalytically active metals, such as platinum (Rewick et al. 1974, Stevens and Dahn 2005), whereby several weight percent of platinum on carbon can increase the gas-phase oxidation rate by orders of magnitude. This, however, is not the case for the electrochemical oxidation of carbon blacks, where at potentials of 0.8 V and higher (vs. RHE) the carbon corrosion rate is within a factor of 2 between that for noncatalyzed and platinum-catalyzed carbon blacks (Roen et al. 2004, Passalacqua et al. 1992, Kinoshita 1988). Therefore, gas-phase oxidation tests to screen potential carbon-black supports is not a reliable method for predicting their stability in the electrochemical environment, so it is essential to measure the carbon corrosion rates directly in an electrochemical cell. 

At present there are no alternative cathode electrocatalysts to platinum. Some platinum alloy electrocatalysts prepared on traditional carbon black supports offer a 25 mV performance gain compared with Pt electrocatalysts. However, only the more stable Pt-based metal alloys, such as PtCr, PtZr, or PtTi, can be used in PEMFC, due to dissolution of the base metal by the perfluorinated sulfonic acid in the electrocatalyst layer and membrane [26]. The focus of the continued search for the elusive electrocatalyst for oxygen reduction in acid environment should be on development of materials with required stability and greater activity than Pt. 

In order to decrease the mass transport limitations encountered in PEMFC electrodes, which are prepared with Pt/carbon black catalysts, it was recently proposed to replace the classical carbon black support by carbon xerogels [2], i.e. nanostmctured materials with well defined pore texture prepared by evaporative drying and pyrolysis of organic gels. Carbon xerogels allow for better gas/water diffusion within the pore texture of the electrode and better contact between the platinum particles and the ionomer (Nafion ). 

Phosphoric Acid Fuel Cell This type of fuel cell was developed in response to the industiy s desire to expand the natural-gas market. The electrolyte is 93 to 98 percent phosphoric acid contained in a matrix of silicon carbide. The electrodes consist of finely divided platinum or platinum alloys supported on carbon black and bonded with PTFE latex. The latter provides enough hydrophobicity to the electrodes to prevent flooding of the structure by the electrolyte. The carbon support of the air elec trode is specially formulated for oxidation resistance at 473 K (392°F) in air and positive potentials. 

It was found in the 1960s that disperse platinum catalyst supported by certain oxides will in a number of cases be more active than a similar catalyst supported by carbon black or other carbon carrier. At platinum deposits on a mixed carrier of WO3 and carbon black, hydrogen oxidation is markedly accelerated in acidic solutions (Hobbs and Tseung, 1966). This could be due to a partial spillover of hydrogen from platinum to the oxide and formation of a tungsten bronze, H WOj (0 < a < 1), which according to certain data has fair catalytic properties. 

It was seen when studying mixed systems Pt-WOj/C and Pt-Ti02/C that with increasing percentage of oxide in the substrate mix the working surface area of the platinum crystallites increases, and the catalytic activity for methanol oxidation increases accordingly. With a support of molybdenum oxide on carbon black, the activity of supported platinum catalyst for methanol oxidation comes close to that of the mixed platinum-ruthenium catalyst. 

The electrochemical reactions occur on highly dispersed electrocatalyst particles supported on carbon black. Platinum (Pt) or Pt alloys are used as the catalyst at both electrodes. 

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... 

From the very beginning of fuel cell development, soot and other active carbons because of their high internal surface, amounting typically to 100 m2/g, had been the most important catalyst supports for fuel cell electrodes. Platinum can be utilized on soot to a higher extent than in the form of dispersed platinum as Pt black. Carbon-supported platinum is the fuel cell catalyst of choice for the cathode as well as for the anode (135, 136). 

The pressed-salt method can be used to overcome this difficulty because it can be used to observe spectra of carbon monoxide on platinum particles which are not supported on silica or alumina (14)- It is possible to use commercial platinum black, but best results are obtained if the platinum particles are formed by reduction of chloroplatinic acid while it is dispersed on the powdered salt. After reduction in hydrogen at 300° C., the sample was treated with CO and transferred to the die. An essential feature of this technique is a final treatment with CO after the sample is in the die. The die is sealed with Apiezon Q wax to prevent exposure to the atmosphere between the time of the final treatment with CO and the application of pressure to form the salt disk. 

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