Applications for PEMFC

Owing to the high electrical conductivity and the known stability of ITO, this material is particularly interesting for fuel cell catalyst supports. It has been proposed as an alternative material for the cathode support in PEMFCs that could avoid the corrosion problems experienced by conventional carbon supports. However, the application for PEMFC catalyst supports is novel and there are few reported works... 

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]. 

In this study, we developed microchannel PrOx reactor to control CO outlet concentrations less than 10 ppm from methanol steam reformer for PEMFC applications. The reactor was developed based on our previous studies on methanol steam reformer [5] and the basic technologies on microchaimel reactor including design of microchaimel plate, fabrication process and catalyst coating method were applied to the present PrOx reactor. The fabricated PrOx reactor was tested and evaluated on its CO removal performance. 

While the PEM fuel cells appear to be suitable for mobile applications, SOFC technology appears more applicable for stationary applications. The high operating temperature gives it flexibility towards the type of fuel used, which enables, for example, the use of methane. The heat thus generated can be used to produce additional electricity. Consequently, the efficiency of the SOFC is -60 %, compared with 45 % for PEMFC under optimal conditions. 

The stability of electrocatalysts for PEMFCs is increasingly a key topic as commercial applications become nearer. The DoE has set challenging near-term durability targets for fuel cell technology (automotive 5,000 h by 2010 stationary 40,000 h by 2011) and has detailed the contribution of the (cathode) catalyst to these. In particular, for automotive systems as well as steady-state stability, activity after simulated drive cycles and start-stop transients has been considered. In practice, both these treatments have been found to lead to severe degradation of the standard state-of-the-art Pt/C catalyst, as detailed next. 

Lee, J., Seo, J., Han, K., and Kim, H. Preparation of low Pt loading electrodes on Nation (Na+)-bonded carbon layer with galvanostatic pulses for PEMFC application. Journal of Power Sources 2006 163 349-356. 

Wilkinson, D. R and St-Pierre, J. 2003. Durability for PEMFC. In Handbook of fuel cells—Fundamentals, technology and applications, part 3, ed. W. Vielstich, A. Lamm and H. A. Gasteiger, 611. Ghichester, England John Wiley Sons. 

The efficiency of PEMFCs ranges from about 40 to 50%, and operating temperature is about 255 K. The PEMFCs and direct methanol fuel cells (DMFCs) are considered to be promising power sources, especially for transportation applications. The PEMFCs with potentially much higher efficiencies and almost zero emissions offer an attractive alternative to the internal combustion engines for automotive applications. This fuel cell has many important attributes such as high efficiency, clean, quiet, low-temperature operation, capable of quick start-up, no liquid electrolyte and simple cell design (Hu et al., 2004). 

In an acidic medium, a PEMFC fed with ethanol allows power densities up to 60 mW cm to be reached at high temperatures (80-120 °C), but this needs platinum-based catalysts, which may prevent wider applications for portable electronic devices. On the other hand, in an alkaline medium, the activity of non-noble catalysts for ethanol or ethylene glycol oxidation and oxygen reduction is sufficient to reach power densities of the order of 20 mW cm at room temperature. This opens up the hope of developing SAMFCs that are particularly efficient for large-scale portable applications. 

S. H. D. Lee, R. Kumar and M. Krumpelt, Removal of CO from Reformate for PEMFC Application. National Technical Information Service, Springfield, VA, 2001. 

Higher operating temperature membranes enable more efficient heat recovery for stationary applications of PEMFCs. 

UTC Fuel Cells has partnered with Shell Hydrogen to develop a variety of fuel processors for natural gas, gasoline, and diesel feed for PEMFC, phosphoric acid fuel cell (PAFC), and distributed H2 production applications.8... 

The thermodynamic calculations on the basis of Equations 5.6-5.8 indicate that ZnO might be unable to reduce the sulfur in the reformate to the level for PEMFC applications when the fuel gas contains a large amount of H20, CO, and C02 due to the thermodynamic factor. ZnO is not efficient for removing COS. It needs to catch more close attention to the effects of the coexisting H20, CO, and C02 on the H2S removal from the reformate in the design of a post-desulfurization process in a hydrocarbon fuel processor, especially at high temperature. 

Taylor et al.8 were the first to report an electrochemical method for preparation of MEAs for PEMFCs. In their technique, Pt was electrochemically reduced and deposited at the electrode membrane interface, where it was actually utilized as an electrocatalyst. Nation, which is an ion exchange polymer membrane, is first coated on a noncatalyzed carbon support. The Nafion-coated carbon support is then immersed into a commercial acidic Pt plating solution for electrodeposition. Application of a cathodic potential results in diffusion of platinum cations through the active Nation layer. The migrated platinum species are reduced and form Pt particle at the electrode/membrane interface only on the sites which are both electronically and ionically conductive. The deposition of Pt particles merely at the electrode/membrane interface maximizes the Pt utilization. The Pt particles of 2-3.5 nm and a Pt loading of less than 0.05 mg cm-2 were obtained employing this technique.8 The limitation of this method is the difficulty of the diffusion of platinum... 

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