Cabot Fuel Cells

Spray pyrolysis routes have been extensively investigated to prepare Pt-based catalysts. Typically, a liquid feed of metal precursor and carbon is atomized into an aerosol and fed into a continuous furnace to evaporate and heat-treat to form a collectable powder. The method has good control over final aggregate particle size and metal particle size distributions, as well as producing powder without further isolation or separation. Hampton-Smith et al. have reviewed efforts of Superior MicroPowder (now Cabot Fuel Cells) in this area. ... 

For the support material of electro-catalysts in PEMFC, Vulcan XC72(Cabot) has been widely used. This carbon black has been successfully employed for the fuel cell applications for its good electric conductivity and high chemical/physical stability. But higher amount of active metals in the electro-catalysts, compared to the general purpose catalysts, make it difficult to control the metal size and the degree of distribution. This is mainly because of the restricted surface area of Vulcan XC72 carbon black. Thus complex and careM processes are necessary to get well dispersed fine active metal particles[4,5]. 

A wide range of carbon blacks is available from a number of suppliers (e.g., Cabot, Columbian Chemicals, Azko Nobel, Denka, Timcal, Degussa, Mitsubishi). Blacks for fuel cell use fall into three general categories ... 

Another important parameter that has to be taken into account when choosing the appropriate diffusion layer is the overall cost of the material. In the last few years, a number of cost analysis studies have been performed in order to determine fuel cell system costs now and in the future, depending on the power output, size of the system, and number of xmits. Carlson et al. [1] reported that in 2005 the manufacturing costs of diffusion layers (for both anode and cathode sides) corresponded to 5% of the total cost for an 80 kW direct hydrogen fuel cell stack (assuming 500,000 units) used in the automotive sector. The total value for the DLs was US 18.40 m-, which included two carbon cloths (E-TEK GDL LT 1200-W) with 27 wt% P ILE, an MPL with PTFE, and Cabot carbon black. Capital, manufacturing, tooling, and labor costs were included in the total. 

Alcaide F, Brillas E, Cabot PL, Casado J. Electrogeneration of hydroperoxide ion using an alkaline fuel cell. J Electrochem Soc 1998 145 3444-3449. 

The individual graphitic layers are the basic building blocks of carbon black particles. The morphology and particle size distribution of carbon black is dependent on the source material and the process of its thermal decomposition. Particle size and distribution determine directly the specific surface area (SSA) which is one of the most important properties of carbon black for fuel cell applications. High surface area (ranging from a few hundreds to 2000-3000m2 g-1) carbon blacks suitable for fuel cell applications can be obtained from Cabot Corporation (Vulcan XC-72R, Black Pearls BP 2000), Ketjen Black International, Chevron (Shawinigan), Erachem and Denka. 

Alcaide, R, Cabot, P.L., and Brillas, E., Fuel cells for chemicals and energy cogeneration, Journal of Power Sources, 2006, 153, 47-60. 

Alcaide, F., Brillas, E., Cabot, P-L. (2004). Limiting behaviour during the hydroperoxide ion generation in a flow alkaline fuel cell. /. Electroanalytical Chem. 566, 235-240. 

Carbons black includes several types of carbons, such as acetylene black, channel black, furnace black, lamp black. Commonly, their names are referred to the process or the source material from which they are made. Among those, the production of furnace black is the most important. Its production process consists in feeding a furnace with natural gas and aromatics oils as feedstock, where is vaporized and then pyrolyzed. Vulcan XC-72 (a furnace black from Cabot Corporation) is the most widely used catalyst support for low-temperature fuel cells due to their low cost and high availability, being this material used as standard to compare other types of carbons. Vulcan XC-72, formed by nanoparticles of 20-40 nm, has an electrical conductivity of 4 S cm a sulphur content of 0.05 %, and a negligible oxygen content [13]. Within the textural properties Vulcan carbon has a superficial area of 252 m g with a total pore volume of 0.63 cm g and a pore size distribution around 15 nm [14]. 

Fig. 19.9 Fuel cell testing of PtML/Pd/C catalyst from scale-up synthesis by Cabot, 50 cm MEAs, 80 °C, 100 % RH, 30 psig back pressure, and 10 min/point [52]...

Velazquez-Palenzuela A, Zhang L, Wang L, Cabot PL, Brillas E, Tsay K, Zhang J (2011) Fe-Nx/C electrocatalysts synthesized by pyrolysis of Fe(II)-2,3,5,6-tetra(2-pyridyl)pyrazine complex for PEM fuel cell oxygen reduction reaction. Electrochim Acta 56 4744 752... 

Cabot s Dynalyst family of electrocatalysts is designed for use in applications ranging from cost-sensitive to performance-driven PEM fuel cell applications. Dynalyst electrocatalyst powders are manufactured to meet specific performance requirements based on their structure, composition and precious metal loading in the electrode layers. Dynalyst 20SR1 - 20% Pt/C electrocatalyst has excellent electrochemical performance at low precious metal loadings in the MEA. A loading of 0.1-0.3 mg Pt/cm in the electrode layer is recommended to achieve optimum performance and Pt utilization. 

Figure 20.6. Performance of a spray-manufactured electrocatalyst polarization and power density curves for a single MEA PEM fuel cell with a 20 wt% Pt/Shawinigan black electrocatalyst employed as cathode catalyst at 0.2 mg Pt/cm loading. Performance measured at 50 °C at atmospheric pressure in a 50 cm cell at constant flow corresponding to stoichiometry of 1.2 for hydrogen and 2.2 for air at 1 A/cm, and with 100% humidification of the gases, Nation 112 membrane. (Reproduced with permission of Cabot CorporatioiL)...

Aiming to deepen into the surface chemistry of typical PEMFC commercial catalysts, a widely used commercial sample of Pt (20wt.%) on Vulcan XC72 catalyst from E-TEK and Vulcan XC72 carbon black from Cabot Corp., have been used for the study and taken as reference materials. The surface diffusion processes associated with hydrogen and oxygen adsorbed species in this catalyst and in PEM fuel cell electrodes prepared with Vulcan XC72 have been examined in detail. 

The other studies of nonbulk metal HOR in alkaline come from Cabot et al. [25,44] who used a Pt-containing gas diffusion electrode (GDE) to closely represent the electrodes of a fuel cell in their RDE experiments. They concluded that at low overpotentials (near the OCV). the Tafel reaction is the rate-determining step in a Tafel-Volmer mechanism, with the diffusion of H2 becoming rate determining at higher overpotentials. These studies also showed that the exchange current density for HOR is lower in alkaline media for GDE. 

In the case of direct methanol fuel cells, compared with oxygen reduction, methanol oxidation accounts for the main activation loss because this process involves six-electron transfer per methanol molecule and catalyst self-poison when Pt alone was used from the adsorbed intermediate products such as COads-From the thermodynamic point of view, methanol electrooxidation is driven due to the negative Gibbs free energy change in the fuel cell. On the other hand, in the real operation conditions, its rate is obviously limited by the sluggish reaction kinetics. In order to speed up the anode reaction rate, it is necessary to develop an effective electrocatalyst with a high activity to methanol electrooxidation. Carbon-supported (XC-72C, Cabot Corp.) PtRu, PtPd, PtW, and PtSn were prepared by the modified polyol method as already described [58]. Pt content in all the catalysts was 20 wt%. 

Such problems forced fuel cell developers to pursue a trade-off between the surface area and the degree of graphitization of the support material. In view of this, Vulcan XC-72 from M/s Cabot Corporation is arguably the most popular catalyst support material. Vulcan XC-72 is basically a high surface area furnace black with reasonably good graphite content. This allows the support material tb be corrosion resistant at PAFC cathode environment. Various properties of Vulcan XC-72 are provided in Table 1. 

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