Fuel cells cathode materials

Strasser, P., Gorer, S., Devenney, M., Electrochemical techniques for the discovery of new fuel-cell cathode materials. In Direct Methanol Fuel Cells, Vol. 4, Narayanan, S.G., Zawodzinski, T. (eds.), The Electrochemical Society Washington, 2001, p 191. 

P. Stonehart and J. P. MacDonald, Stability of Acid Fuel Cell Cathode Materials, Electric Power Research Institute Report EM-1664, 1981. 

J.R. Wilson, D.T. Schwartz, S.B. Adler, Nonlinear electrochemical impedance spectroscopy for solid oxide fuel cell cathode materials, Electrochim. Acta, 2006,51, pp.1389-1402. 

Cathode The carbonate fuel cell cathode material has been lithiated NiO from the beginning of development This component is known to have a small but finite solubility in the electrolyte. The extent of its dissolution is controlled mainly by electrolyte composition, applied gas atmosphere, operation pressure and temperature. Some developers have selected an atmospheric pressure system to assure minimal dissolution and adequate long-term life for the cathode. Long-term field operation has shown no issues relating to particle coarsening, indicating a stable structure (Fig. 9). 

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... 

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. 

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. 

Figure 2. Fuel Cell Stack Material Cost versus Cathode Platinum Loading...

Lanthanoid manganites, such as LaMnOj, NdMnOj and GdMnOj, are of potential value in solid oxide fuel cell cathodes. However, many of these phase show thermal contraction because of the diminishing Jahn-Teller distortion of the Mtf " cations as the temperature is increased. Such effects tend to rule out these materials for real cell applications, although A- and B-site substitution, as demonstrated for PbTiOj earlier, can ameliorate the problem. 

Strontium-doped lanthanum manganite synthesis for solid oxide fuel cells cathode. Journal of New Materials for Electrochemical Systems, Vol. 12, No. 2-3, (1 April 2009), pp. (109-113), ISSN 1480-2422... 

At the current stage of technology, carbon-supported Pt and Pt-based alloy catalysts are the most active and stable catalysts for an ORR, which have been used for fuel cell cathodes. The major research effort for Pt and Pt-based alloy cattdysts is to optimize (1) the size and dispersion of nanoparticles, (2) interaction between Pt catalyst and supporting materials, and (3) Pt-alloying strategy. 

Zelenay et al. explored Co-polypyrrole (CoPPy) material as a PEM fuel-cell cathode catalyst. The composite CoPPy catalyst, even without a heat treatment, could generate a power density of 0.15Wcm in a H2—O2 fuel cell and displayed no signs of performance degradation for more than 100 h. Their results showed that heteroatomic polymers can be used not only to stabilize the non-noble metals in a PEM fuel cell environment but also to generate active sites for the ORR. Study of the interaction between the catalyst and oxygen also demonstrated that CoPPy... 

In spite of a very significant progress achieved with heat-treated macrocyclic compounds as ORR catalysts since the early 1970s, the activity and durability of that family of catalysts are stiU insufficient for replacing platinum at the fuel cell cathode and in other applications. Furthermore, the complex structure of macrocyclic compounds makes their synthesis expensive and potentially noncompetitive with precious-metal-based catalysts also from the materials cost point of view. For those reasons, much effort has been invested by the electrocatalysis research community in recent years into finding less expensive and catalytically more active non-precious metal ORR catalysts that would not rely on macrocylic compounds as either catalysts or catalyst precursors. In the past decade, there has been a significant improvement both in the activity and of non-macrocyclic catalysts, expected to be manufactured at a fraction of the cost of their macrocyclic counterparts. In this section, we review the precursors, synthesis routes, and applications of this relatively new family of catalysts. 

This chapter is devoted, in particular, to metal carbides in fuel cell cathode as potential alternative materials to conventional carbon support owing to their bifunctional capability, catalysts and catalyst supports. 

Severe carbon corrosion produces carbon dioxide and results in the loss of the carbon material as shown by Eq. 11. For a fuel cell cathode containing 0.6 mg cm of carbon, a simple calculation according to the Faraday s law shows how many hours the carbon can last before it is completely corroded. The results are shown in Table 1. It is striking to see that the carbon corrosion current density needs to be less than 0.15 pA cm in order for the carbon to last for 40,000 hours. If we assume that the electrode wlU not function properly when 20% of carbon is corroded, then a corrosion current density should be lower than 0.03 pA cm. ... 

Skinner, S.J. (2001). Recent Advances in Perovskite-type Materials for Solid Oxide Fuel Cell Cathodes. International Journal of Inorganic Materials, Vol. 3, (March 2001), pp. 113-121, ISSN 1466-6049... 

Chroneos A, Yildiz B, Tarancon A, Parfitt D, Kilner JA (2011) Oxygen diffusion in solid oxide fuel cell cathode and electrolyte materials mechanistic insights from atomistic simulations. Energ Environ Sci 4 2774... 

Fergus JW (2006) Oxide anode materials fin solid oxide fuel cells. Solid Stale Ionics 177 1529 Fleig J (2003) Solid oxide fuel cell cathodes polarization mechanisms and modeling of the electrochemical performance. Aimu Rev Mafin Res 33 361-382 Gellings PJ, Bouwmeester HIM (2000) Solid stale aspects of oxidatitm catalysis. Catal Today 58 1-53... 

Fleig, J., Solid Oxide Fuel Cell Cathodes Polarization Mechanisms and Modeling of the Electrochemical Performance. Annual Review of Materials Research, 2003. 33 p. 361 - 382. 

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