Direct methanol fuel cells proton exchange membranes

Low-temperature fuel cells proton exchange membrane fuel cells (PEMFCs) and direct methanol fuels (DMFCs)... 

Proton exchange membranes (PEMs) are one of the key materials in low-temperature fuel cells proton exchange membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMECs). Especially, recent trend in the research and development of low-temperamre fuel cells focuses on PEMFCs for transportation (electric vehicle) applications due to the impact on economy and environment. The most important role of PEMs is to transport protons formed as a product of oxidation reaction of fuels at the anode to the cathode, where oxygen reduction reaction takes place to produce water. In addition to this, there are a number of requirements for PEM materials for the practical fuel cell applications, which include... 

Sua, Y., Liu, Y., Suna, Y., Lai, J., Wang, D., Gaoe, Y., liu, B., Guiver, M.D. (2007) Proton exchange membranes modified with sulfonated silica nanoparticles for direct methanol fuel cells. Journal of Membrane Science, 296, 21-28. 

Two types of fuel cells that employ polymeric cation exchange membranes as the electrolyte material are the proton exchange membrane fuel cell (PEMFC) and the direct methanol fuel cell (DMFC). The membrane has a multifunchonal role in these devices ... 

The electrocatalytic oxidation of methanol has been widely investigated for exploitation in the so-called direct methanol fuel cell (DMFC). The most likely type of DMFC to be commercialized in the near future seems to be the polymer electrolyte membrane DMFC using proton exchange membrane, a special form of low-temperature fuel cell based on PEM technology. In this cell, methanol (a liquid fuel available at low cost, easily handled, stored, and transported) is dissolved in an acid electrolyte and burned directly by air to carbon dioxide. The prominence of the DMFCs with respect to safety, simple device fabrication, and low cost has rendered them promising candidates for applications ranging from portable power sources to secondary cells for prospective electric vehicles. Notwithstanding, DMFCs were... 

There are six different types of fuel cells (Table 1.6) (1) alkaline fuel cell (AFC), (2) direct methanol fuel cell (DMFC), (3) molten carbonate fuel cell (MCFC), (4) phosphoric acid fuel cell (PAFC), (5) proton exchange membrane fuel cell (PEMFC), and (6) the solid oxide fuel cell (SOFC). They all differ in applications, operating temperatures, cost, and efficiency. 

This survey focuses on recent developments in catalysts for phosphoric acid fuel cells (PAFC), proton-exchange membrane fuel cells (PEMFC), and the direct methanol fuel cell (DMFC). In PAFC, operating at 160-220°C, orthophosphoric acid is used as the electrolyte, the anode catalyst is Pt and the cathode can be a bimetallic system like Pt/Cr/Co. For this purpose, a bimetallic colloidal precursor of the composition Pt50Co30Cr20 (size 3.8 nm) was prepared by the co-reduction of the corresponding metal salts [184-186], From XRD analysis, the bimetallic particles were found alloyed in an ordered fct-structure. The elecbocatalytic performance in a standard half-cell was compared with an industrial standard catalyst (bimetallic crystallites of 5.7 nm size) manufactured by co-precipitation and subsequent annealing to 900°C. The advantage of the bimetallic colloid catalysts lies in its improved durability, which is essential for PAFC applicabons. After 22 h it was found that the potential had decayed by less than 10 mV [187],... 

All fuel cells for use in vehicles are based on proton-exchange-membrane fuel cell (PEMFC) technology. The methanol fuel-processor fuel cell (FPFC) vehicle comprises an on-board fuel processor with downstream PEMFC. On-board methanol reforming was a development focus of industry for a number of years until around 2002. Direct-methanol fuel cells (DMFC) are no longer considered for the propulsion of commercial vehicles in the industry (see also Chapter 13). 

Michael Hickner received his B.S. in Chemical Engineering from Michigan Tech in 1999 and his Ph.D. in Chemical Engineering in 2003 under the direction of James McGrath. Michael s research in Dr. McGrath s lab focused on the transport properties of proton exchange membranes and their structure-property relationships. He has spent time at Los Alamos National Laboratory studying novel membranes in direct methanol fuel cells and is currently a postdoc at Sandia National Laboratories in Albuquerque, NM. 

Polyphosphazene-based PEMs are potentially attractive materials for both hydrogen/air and direct methanol fuel cells because of their reported chemical and thermal stability and due to the ease of chemically attaching various side chains for ion exchange sites and polymer cross-linking onto the — P=N— polymer backbone. Polyphosphazenes were explored originally for use as elastomers and later as solvent-free solid polymer electrolytes in lithium batteries, and subsequently for proton exchange membranes. 

SOFC = solid oxide fuel cell MCFC = molten carbonate fuel cell PAFC = phosphoric acid fuel cell AFC = alkaline fuel cell PEMFC = proton exchange membrane fuel cell DMFC = direct methanol fuel cell SAMFC = Solid alkaline membrane fuel cell. 

Direct methanol fuel cell (DMFC) working between 30 and 110 °C with a proton exchange membrane (such as Nafion) as electrolyte, which realizes the direct oxidation of methanol at the anode. 

Fig. 13.27. Potential vs. current density plots for state-of-the-art fuel cells, o, proton exchange membrane fuel cell , solid oxide fuel cell , pressurized phosphonic acid fuel cell (PAFC) a, direct methanol fuel cell, direct methanol PAFC , alkaline fuel cell. (Reprinted from M. A. Parthasarathy, S. Srinivasan, and A. J. Appleby, Electrode Kinetics of Oxygen Reduction at Carbon-Supported and Un-supported Platinum Microcrystal-lite/Nafion Interfaces, J. Electroanalytical Chem. 339 101-121, copyright 1992, p. 103, Fig. 1, with permission from Elsevier Science.)...

PEMFC (Proton Exchange Membrane Fuel Cell) and SPFC (Solid Polymer Fuel Cell) are the two competing mnemonics of a low-temperature fuel cell type originated for use in space by General Electric, USA. To reflect present practice, the author will use PEFC (Proton Exchange Fuel Cell). The DMFC (Direct Methanol Fuel Cell) also uses proton exchange membranes, but is referred to by its own mnemonic. Proton exchange between polar water molecules is discussed by Koryta (1991 1993) and in the introduction to this book. 

Pt-based electrocatalysts are usually employed in proton exchange membrane fuel cells (PEMFC) and direct methanol fuel cells (DMSC). In direct-methanol fuel cells (DMFCs), aqueous methanol is electro-oxidized to produce COj and electrical current. To achieve enhanced DMFC performance, it is important to develop electrocatalysts with higher activity for methanol oxidation. Pt-based catalysts are currently favored for methanol electro-oxidation. In particular, Pt-Ru catalysts, which gave the best results, seem to be very promising catalysts for this application. Indeed, since Pt activates the C-H bounds of methanol (producing a Pt-CO and other surface species which induces platinum poisoning), an oxophilic metal, such as Ru, associated to platinum activates water to accelerate oxidation of surface-adsorbed CO to... 

Methanol, CH3OH, may eventually be used directly in a fuel cell without the extra step of reforming to Hj. Such fuel cells are similar to proton exchange membrane fuel cells and are called direct methanol fuel cells (cf. sec-... 

In general, because PAFCs are proton conductors like the proton exchange membrane (PEM) and the subcategory direct methanol fuel cells (sections 3.5 and 3.6), there is a continuous conceptual transition between them. The polymers used in PEM cells usually contain weakly acidic components such as HSO3, but may be reinforced with a stronger acid in order to increase conductivity or allow operation at higher temperatures. 

This survey focuses on recent catalyst developments in phosphoric acid fuel cells (PAFC), proton exchange membrane fuel cells (PEMFC), and the previously mentioned direct methanol fuel cell (DMFC). A PAFC operating at 160-220 °C uses orthophosphoric acid as the electrolyte the anode catalyst is Pt and the cathode can... 

PEMFC (proton exchange membrane) uses fluoropolymer or similar type membranes such as SPEEK. Microbial and direct methanol fuel cells fall into this category also. 

The only deviation from this pattern is the DMFC (direct methanol fuel cell) which uses methanol as a fuel without intermediate reforming and microbial fuel cells that use sugar as a fuel and derive current from the metabolic activity of yeast. Both types use a solid ion exchange membrane type electrolyte (proton exchange membrane). 

Hickner, M., Wang, F., Kim, Y. et al. (2001) Chemistry-morphology-property relationships of novel proton exchange membranes for direct methanol fuel cells, ACS Fuel (Part 1), Vol. 222, August 26—30, Chicago, p. 51. 

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