Fuel cell cathodes

The first reported electroorganic synthesis of a sizeable amount of material at a modified electrode, in 1982, was the reduction of 1,2-dihaloalkanes at p-nitrostyrene coated platinum electrodes to give alkenes. The preparation of stilbene was conducted on a 20 pmol scale with reported turnover numbers approaching 1 x 10. The idea of mediated electrochemistry has more frequently been pursued for inorganic electrode reactions, notably the reduction of oxygen which is of eminent importance for fuel cell cathodes Almost 20 contributions on oxygen reduction at modified... 

In case of fuel cell cathodes, theoretical considerations were directed towards optimizing catalysts for O2 reduction [103]. This has led to the synthesis of Pt3Co/C nanocatalyst systems and preliminary results again indicate perfect agreement between the calculations and the wet electrochemical results obtained with metal nanoparticles of the composition which theory had recommended [106]. 

ELECTROCATALYSIS OF OXYGEN REDUCTION IN THE FUEL CELL CATHODE NEW INSIGHTS AND NEW OUESTIONS... 

With the four-electron ORR process in the fuel cell cathode well recognized as the principal challenge at both the theoretical and experiniental/technical levels, it is interesting to examine the effects of the most recent theoretical developments on the fundamental understanding of ORR electrocatalysis. Such examination would naturally focus on the nature and quahty of the links with experimental work, as reflected by ... 

Paradoxically, all these significant recent contributions to the theory of the ORR, together with most recent experimental efforts to characterize the ORR at a fuel cell cathode catalyst, have not led at aU to a consensus on either the mechanism of the ORR at Pt catalysts in acid electrolytes or even on how to properly determine this mechanism with available experimental tools. To elucidate the present mismatch of central pieces in the ORR puzzle, one can start from the identification of the slow step in the ORR sequence. With the 02-to-HOOads-to-HOads route appearing from recent DFT calculations to be the likely mechanism for the ORR at a Pt metal catalyst surface in acid electrolyte, the first electron and proton transfer to dioxygen, according to the reaction... 

Proper answers to the above questions can be provided once it is realized that the surface of the catalyst in a fuel cell cathode using a Pt or Pt/C catalyst cannot be... 

Nprskov JK, Rossmeisl J, Logadottir A, Lindqvist L, Kitchin JR, Bligaard T, Jonsson H. 2004. Origin of the overpotential for oxygen reduction at a fuel-cell cathode. J Phys Chem B 108 17886-17892. 

Such bimetallic alloys display higher tolerance to the presence of methanol, as shown in Fig. 11.12, where Pt-Cr/C is compared with Pt/C. However, an increase in alcohol concentration leads to a decrease in the tolerance of the catalyst [Koffi et al., 2005 Coutanceau et ah, 2006]. Low power densities are currently obtained in DMFCs working at low temperature [Hogarth and Ralph, 2002] because it is difficult to activate the oxidation reaction of the alcohol and the reduction reaction of molecular oxygen at room temperature. To counterbalance the loss of performance of the cell due to low reaction rates, the membrane thickness can be reduced in order to increase its conductance [Shen et al., 2004]. As a result, methanol crossover is strongly increased. This could be detrimental to the fuel cell s electrical performance, as methanol acts as a poison for conventional Pt-based catalysts present in fuel cell cathodes, especially in the case of mini or micro fuel cell applications, where high methanol concentrations are required (5-10 M). 

Jasinski R. 1964. A new fuel cell cathode catalyst. Nature 201 1212. 

Liu, X., Chen, J., Liu, G., Zhang, L., Zhang, H., and Yi, B. (2010) Enhanced long-term durability of proton exchange membrane fuel cell cathode by employing Pt/Ti02/C catalysts. Journal of Power Sources, 195 (13), 4098-4103. 

Fuel Cells Cathode and anode catalyst support Intercell connectors... 

Bansal NP and Zhong Z. Combustion synthesis of Sm0 5Sr0 5Co03 x and Lao 6Sr04CoO3 x nanopowders for solid oxide fuel cell cathodes. J. Power Sources 2006 158 148-153. 

Although platinum is the metal of choice for PEM fuel cell cathodes, Paul Matter, Elizabeth Biddinger, and Umit Ozkan (Ohio State University) show that nonprecious metals will have to be developed for this type of fuel cell to become practical and widely used. Although few materials have the electrochemical properties needed to replace platinum, this review discusses candidates such as macrocycle compounds, non-marcrocyclic pyrolyzed carbons, conducting polymers, chalcogen-ides, and heteropolyacids. 

Alternative cathode catalysts to platinum have been the focus of many researchers over the past four decades. Numerous reviews have been published on various aspects and types of PEM fuel cell cathode catalysts.2,7-21 In this work we review the major classes of non-noble metal ORR catalysts in acidic electrolytes. The techniques used to study the catalysts, a brief history of catalyst development including major breakthroughs, and possible future directions will be discussed. 

Despite the uncertainty regarding the exact nature of the active site for oxygen reduction, researchers have managed to produce catalysts based on heat-treated macrocycles with comparable activities to state-of-the-art platinum catalysts. In numerous cases researchers have shown activity close to or better than platinum catalysts.64,71,73,103,109 Since the active site for the ORR in these materials is not fully understood, there is still potential for breakthrough in their development. Another advantage of this class of materials that should be mentioned is their inactivity for methanol oxidation, which makes them better suited than platinum for use in direct methanol fuel cell cathodes where methanol crossover to the cathode can occur.68,102,104,122-124 While the long-term activity of heat treated materials is... 

Polymers have served roles in PEM fuel cell cathodes such as modifiers to macrocycle-based electrodes to improve conductivity and stability,165 composite materials with heteropolyacids,166 and as precursors to pyrolyzed catalysts.38,112,132,133 However, as discussed in the previous section, the activity of nitrogen-containing carbon raises the possibility of non-metal electrodes functioning in a cathode environment. Likewise, researchers have noted ORR activity for various conducting polymers containing nitrogen, and recently studies on their potential use in PEM fuel cell cathodes have been reported. 

Research on alternative catalysts for the ORR for use in PEM fuel cell cathodes is an exciting and growing field of research. Several classes of materials show potential for replacing precious metal cathodes, especially for automotive power applications and direct methanol systems. Increasing the understanding of active sites in alternative catalysts, the mechanisms for oxygen reduction, and optimization of full fuel cell preparation using alternative materials, will lead to further improvements in performance. 

Fischer-Tropsch, 178 for back-bonding, 17 for direct bonding, 17 formic acid, 141 FTIR characterizations, 291 fuel cell, 47, 185, 290, 320 fuel cell catalyst, 290 fuel cell cathode reactions, 303... 

In fuel cells, the combustion energy of hydrocarbons can be converted directly into electrical energy. At the fuel cell anode, the hydrocarbon is in most cases converted to carbon dioxide because the intermediates are more easily oxidized than the starting hydrocarbon (Eq. 9a) at the fuel cell cathode oxygen is reduced to water (Eq. 9b). Most fuel cell research has involved the use of hydrogen as fuel. However, solid oxide fuels cells (SOCFs) can operate at higher temperature and can... 

P.N. Ross, "Anomalous Current Ratios in Phosphoric Acid Fuel Cell Cathodes," LBL-13955 submitted toJ. Electrochem. Soc., March 1986. 

Ambient air (stream 200) is compressed in a two-stage compressor with intercooling to conditions of approximately 193°C (380°F) and 8.33 atmospheres (122.4 psia). The majority of the compressed air (stream 203) is utilized in the fuel cell cathode however, a small amount of... 

The spent fuel is completely combusted in the anode exhaust converter. This flue gas mixture is fed directly to the fuel cell cathode. The cathode exhaust has significant usable heat, which is utilized in the fuel cleanup and in steam generation. The residual heat can be utilized to heat air, water, or steam for cogeneration applications. Design parameters for the IR-MCFC are presented in Table 9-9. Overall performance values are presented in Table 9-10. 

Ambient air (stream 10) is compressed to 15.1 atmospheres and 409°C (275°F) (stream 11), and subsequently heated to 579°C (1075°F) prior to entering the high-pressure fuel cell cathode (stream 12). 

A typical cyclic voltammogram obtained from a fuel cell cathode is shown in Figure 2.3. From this figure, the can be obtained using the... 

Ramesh, P, Itkis, M. E., Tang, J. M., and Haddon, R. C. SWNT-MWNT hybrid structure for proton exchange membrane fuel cell cathodes. Journal of Physical Chemistry C 2008 112 9089-9094. 

Wang, G., Mukherjee, P P, and Wang, C. Y. Optimization of polymer electrolyte fuel cell cathode catalyst layers via direct numerical simulation modeling. Electrochimica Acta 2007 52 6367-6377. 

Jain, P, Biegler, L. T., and Jhon, M. S. Optimization of polymer electrolyte fuel cell cathodes. Electrochemical and Solid-State Letters 2008 1LB193-B196. 

Passos, R. R., Paganin, V. A., and Ticianelli, E. A. Studies of the performance of PEM fuel cell cathodes with the catalyst layer directly applied on Nation membranes. Electrochimica Acta 2006 51 5239-5245. 

Song, Y, Wei, Y, Xu, H., Williams, M., Liu, Y., Bonville, L. J., Kunz, H. R., and Fenton, J. M. Improvement in high-temperature proton exchange membrane fuel cells cathode performance with ammonium carbonate. Journal of Power Sources 2005 141 250-257. 

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