Fuel PEMFC

Schematic diagram of a hydrogen-fueled, PEMFC system for automotive applications. (Reproduced with permission from Elsevier Ahluwalia, R.K., and Wang, X., /. Power Sources, 139(1-2), 152-164, 2005.)...

COPICO-CAS. Development of a domestic cogeneration system based on the use of a PEM using natural gas as input fuel (PEMFC). 

A DMFC is quife similar to a proton exchange membrane fuel (PEMFC) in stack structure and components. They both use a PEM for transporting the protons and Pt-based catalysts at the cathode. The anode catalyst for a DMPC is typically a Pt-Ru alloy that has higher CO tolerance than Pt alone, and this is similar to the PEMFC when H2 contains trace amounts of CO. In fhe infer-mediate sfeps during methanol oxidation, some CO-like species will form, which can seriously poison the anode catalyst. The presence of Ru helps fhe removal of fhe CO-like species from fhe Pt surface trough Reaction 7.6. 

The commercialization of proton exchange membrane fiiel cells (PEMFCs) is now challenged by the high cost of noble metal catalysts such as Pt. For H2 fueled PEMFCs, H2 oxidation is rapid at the Pt anode whereas the oxygen reduction is slow at the Pt cathode. In addition to the attempts to facilitate the electrocatalytic reaction, alloying of Pt as well as replacement of Pt have been pursued. Another attempt is to increase the efficiency of the Pt catalyst and thus to decrease the amount... 

Fig. 9.17 Cell polarization and power density plots for the Fl fueled PEMFCs using various carbon supported (Pt 20 wt%) cathode catalysts (a) fed at 60°C (b) fed at 80°C and (c) air fedat80°C. (From [13])...

Recently, intense academic and industrial research efforts have focused on proton-exchange membrane fuel cells (PEMFC)s due to the promise of commercialization and mass production. In response to the rapid depletion of fossil fuels, PEMFCs use alternative and renewable energy/fuels for zero or minimal pollutant... 

FIG. 6.8 Current-voltage performance of direct fuel PEMFCs (cell temperature 80 °C). (Reprinted with permission from Wiley (2007). Copyright 2007 John Wiley Sons, Inc. [8].)... 

The significant improvement in electrochemical performances of the HMC as an anode in the LIB, electrode material for the EC and cathode catalyst support for Pt in H2-fueled PEMFC are attributed to unique structural properties of the HMC. In particular, the 3D-interconnected nanostructure with hierarchical porosity, providing not only large specific surface area and high mesopore volume for high specific capacitance and homogeneous dispersion of nano-sized Pt and Pt-based alloy nanoparticles but also highly developed hierarchical macro/mesoporosity for fast mass transport. 

The most promising fuel cell for transportation purposes was initially developed in the 1960s and is called the proton-exchange membrane fuel cell (PEMFC). Compared with the PAFC, it has much greater power density state-of-the-art PEMFC stacks can produce in excess of 1 kWA. It is also potentially less expensive and, because it uses a thin solid polymer electrolyte sheet, it has relatively few sealing and corrosion issues and no problems associated tvith electrolyte dilution by the product water. 

Proton Exchange Membrane Fuel Cells (PEMFCs)... 

Propylene glycol, glycolysis of polyurethanes with, 572 Propylene oxide (PO), glycolysis of polyurethanes with, 572-573 Propylene oxide (PO) polyols, 211, 223 Proton exchange membrane fuel cells (PEMFCs), 272-273 Proton NMR integrations, 386. See also H NMR spectroscopy Protonic acids, reactions catalyzed by, 67-68... 

PEMFC proton exchange membrane fuel cell... 

For last few years, extensive studies have been carried out on proton conducting inorganic/organic hybrid membranes prepared by sol-gel process for PEMFC operating with either hydrogen or methanol as a fuel [23]. A major motivation for this intense interest on hybrid membranes is high cost, limitation in cell operation temperature, and methanol cross-... 

Sol-gel techniques have been successfidly applied to form fuel cell components with enhanced microstructures for high-temperature fuel cells. The apphcations were recently extended to synthesis of hybrid electrolyte for PEMFC. Although die results look promising, the sol-gel processing needs further development to deposit micro-structured materials in a selective area such as the triple-phase boundary of a fuel cell. That is, in the case of PEMFC, the sol-gel techniques need to be expanded to form membrane-electrode-assembly with improved microstructures in addition to the synthesis of hybrid membranes to get higher fuel cell performance. 

Development of Highly Compaet PROX System for PEMFC Fuel Processor... 

Electro-catalysts which have various metal contents have been applied to the polymer electrolyte membrane fuel cell(PEMFC). For the PEMFCs, Pt based noble metals have been widely used. In case the pure hydrogen is supplied as anode fuel, the platinum only electrocatalysts show the best activity in PEMFC. But the severe activity degradation can occur even by ppm level CO containing fuels, i.e. hydrocarbon reformates[l-3]. To enhance the resistivity to the CO poison of electro-catalysts, various kinds of alloy catalysts have been suggested. Among them, Pt-Ru alloy catalyst has been considered one of the best catalyst in the aspect of CO tolerance[l-3]. 

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]. 

Fig. 1. Performance evaluation of prepared electro-catalysts as an electrode of PEMFC. Cell temperature 70 C, active area 50cm, platinum loading anode(0.3mgPt/cm )/cathode(0.45mg Pt/cm ), fuel utilization H2/O2 = 80%/50%, RH 100% RFl, pressure H2/O2 = 0 psig/0 psig.

The principle of the fuel cell was first demonstrated by Grove in 1839 [W. R. Grove, Phil. Mag. 14 (1839) 137]. Today, different schemes exist for utilizing hydrogen in electrochemical cells. We explain the two most important, namely the Polymer Electrolyte Membrane Fuel Cell (PEMFC) and the Solid Oxide Fuel Cell (SOFC). 

Interestingly, the PEMFC may also operate directly on methanol. Naturally, the problems associated with high coverage of various intermediates will be present, as mentioned above, as well as additional problems such as loss of methanol over the membrane. Nevertheless, it is possible to operate a methanol fuel cell with a voltage around 0.4 V and a reasonable current, to power small mobile devices such as portable computers and cell phones and make them independent of connection to the conventional power net. For more details on fuel cells we refer the reader to L. Carr-ette, K.A. Friedrich and U. Stimming, Fuel Cells 1(1) (2001) 5-39. 

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. 

PAFC, phosphoric acid fuei ceii MCFC, moiten carbonate fuei ceii SOFC, soiid oxide fuei ceii PEMFC, proton exchange membrane fuei ceii DMFC, direct methanoi fuei ceii AFC, alkaiine fuel cell. 

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