Polymer electrolyte fuel cells diffusion

E. C. Kumbar, K. V. Sharp, and M. M. Mench, A Vahdated Leverett Approach to Multiphase How in Polymer Electrolyte Fuel Cell Diffusion Media Part 3, Temperature Effect and Unified Approach, /. Electrochem. Soc., Vol. 154, pp. B1315 B1324, 2007. 

Higuchi, E., Uchida, H., Fujinami, T., and Watanabe, M. Gas diffusion electrodes for polymer electrolyte fuel cells using borosiloxane electrolytes. Solid State Ionics 2004 171 45-49. 

Paganin, V. A., Ticianelli, E. A., and Gonzalez, E. R. Development and electrochemical studies of gas diffusion electrodes for polymer electrolyte fuel cells. Journal of Applied Electrochemistry 1996 26 297-304. 

Every, H. A., Hickner, M. A., McGrath, J. E. and Zawodzinski, T. A. 2005. An NMR study of methanol diffusion in polymer electrolyte fuel cell membranes. Journal of Membrane Science 250 183-188. 

T. loroi, T. Oku, K. Yasuda, N. Kumagai, and Y. Miyazaki. Influence of PTFE coating on gas diffusion backing for unitized regenerative polymer electrolyte fuel cells. Journal of Power Sources 124 (2003) 385-389. 

N. Holmstrom, J. Ihonen, A. Lundblad, and G. Lindbergh. The Influence of the gas diffusion layer on water management in polymer electrolyte fuel cells. Fuel Cells 7 (2007) 306-313. 

L. Giorgi, E. Antolini, A. Pozio, and E. Passalacqua. Influence of the PIPE content in the diffusion layer of low-Pt loading electrodes for polymer electrolyte fuel cells. Electrochimica Acta 43 (1998) 3675-3680. 

H. Nakajima, T. Konomi, and T. Kitahara. Direct water balance analysis on a polymer electrolyte fuel cell (PEFC) Effects of hydrophobic treatment and microporous layer addition to the gas diffusion layer of a PEFC on its performance during a simulated start-up operation. Journal of Power Sources 171 (2007) 457-463. 

U. Pasaogullari, C. Y. Wang, and K. S. Chen. Two-phase transport in polymer electrolyte fuel cells with bilayer cathode gas diffusion media. Journal of the Electrochemical Society 152 (2005) A1574-A1582. 

E. Antolini, R. R. Passos, and E. A. Ticianelli. Effects of the cathode gas diffusion layer characteristics on the performance of polymer electrolyte fuel cells. Journal of Applied Electrochemistry 32 (2002) 383-388. 

L. R. Jordan, A. K. Shukla, T. Behrsing, et al. Effects of diffusion-layer morphology on the performance of polymer electrolyte fuel cells operating at atmospheric pressure. Journal of Applied Electrochemistry 30 (2000) 641-646. 

G. Inoue, Y. Matsukuma, and M. Minemoto. Evaluation of the thickness of membrane and gas diffusion layer with simplified two-dimensional reaction and flow analysis of polymer electrolyte fuel cell. Journal of Power Sources 154... 

J. T. Gostick, M. W. Fowler, M. A. loannidis, et al. Capillary pressure and hydrophilic porosity in gas diffusion layers for polymer electrolyte fuel cells. Journal of Power Sources 156 (2006) 375-387. 

H. Yamada, T. Hatanaka, H. Murata, and Y. Morimoto. Measurement of flooding in gas diffusion layers of polymer electrolyte fuel cells with conventional flow field. Journal of the Electrochemical Society 153 (2006) A1748-A1754. 

H. Dohle, R. Jung, N. Kimiaie, J. Mergel, and M. Muller. Interaction between the diffusion layer and the flow field of polymer electrolyte fuel cells—Experiments and simulation studies. Journal of Power Sources 124 (2003) 371-384. 

The beginning of modeling of polymer-electrolyte fuel cells can actually be traced back to phosphoric-acid fuel cells. These systems are very similar in terms of their porous-electrode nature, with only the electrolyte being different, namely, a liquid. Giner and Hunter and Cutlip and co-workers proposed the first such models. These models account for diffusion and reaction in the gas-diffusion electrodes. These processes were also examined later with porous-electrode theory. While the phosphoric-acid fuel-cell models became more refined, polymer-electrolyte-membrane fuel cells began getting much more attention, especially experimentally. 

Polymer electrolyte fuel cell (PEFC) is considered as one of the most promising power sources for futurist s hydrogen economy. As shown in Fig. 1, operation of a Nation-based PEFC is dictated by transport processes and electrochemical reactions at cat-alyst/polymer electrolyte interfaces and transport processes in the polymer electrolyte membrane (PEM), in the catalyst layers consisting of precious metal (Pt or Ru) catalysts on porous carbon support and polymer electrolyte clusters, in gas diffusion layers (GDLs), and in flow channels. Specifically, oxidants, fuel, and reaction products flow in channels of millimeter scale and diffuse in GDL with a structure of micrometer scale. Nation, a sulfonic acid tetrafluorethy-lene copolymer and the most commonly used polymer electrolyte, consists of nanoscale hydrophobic domains and proton conducting hydrophilic domains with a scale of 2-5 nm. The diffusivities of the reactants (02, H2, and methanol) and reaction products (water and C02) in Nation and proton conductivity of Nation strongly depend on the nanostructures and their responses to the presence of water. Polymer electrolyte clusters in the catalyst layers also play a critical... 

Figure 6.4. The polarization curves of fuel cells with electrodes that contain various PTFE content in the gas diffusion layer ( ) 10 ( ) 20 (A) 30 (+) 40 wt% [5]. (Reprinted from Journal of Power Sources, 94(1), Song JM, Cha SY, Lee WM. Optimal composition of polymer electrolyte fuel cell electrodes determined by the AC impedance method, 78-84, 2001, with permission from Elsevier and the authors.)...

Pasaogullari, U. and Wang, C.Y, Liquid water transport in gas diffusion layer of polymer electrolyte fuel cells, J. Electrochem. Soc., 151, A399, 2004. 

Figure 3.37. Computed velocity fields (m/s) for flows in adjacent interdigitated oxygen channels (with gas diffusion layer on the left side) of a PEM fuel cell (A inlet, C outlet, in x-y plane). In the middle (B), the flow from one gas channel through the gas diffusion layer to the adjacent gas channel is shown in the z-y plane, for the midpoint of the cell extension in the z-direction. The flows in A and C are for the midpoint value of z. (From S. Um and C. Wang (2004). Three-dimensional analysis of transport and electrochemical reactions in polymer electrolyte fuel cells. /. Power Sources 125, 40-51. Used with permission from Elsevier.)...

Hajbolouri, F. Andreaus, B. Scherer, G.G. Wokaun, A. CO tolerance of commercial Pt and Pt-Ru gas diffusion electrodes in polymer electrolyte fuel cells. Fuel Cells 2004, 4 (3), 160-168. 

Hiramitsu Y, Sato H, Hosomi H, Aoki Y, Harada T, Sakiyama Y, Nakagawa Y, Kobayashi K, Hori M (2009) Influence of humidification on deterioration of gas diffusivity in catalyst layer on polymer electrolyte fuel cell. J Power Sources 195 435-444... 

A typical cross section of a polymer electrolyte fuel cell (PEFQ is sketched in Figure 6.1. The membrane electrode assembly (MEA) is clamped between two metal or graphite plates with the channels for feed gases supply, called the flow field . The MEA usually consists of two gas-diffusion layers (GDLs) and two catalyst layers, separated by proton-conducting membrane. 

The membrane in the polymer electrolyte fuel cell (PEFC) is a key component. Not by chance does the type of membrane brand the cell name - it is the most important component determining cell architecture and operation regime. Polymer electrolyte membranes are almost impermeable to gases, which is crucial for gas-feed cells, where hydrogen (or methanol) oxidation and oxygen reduction must take place at two separated electrodes. However, water can diffuse through the membrane and so can methanol. Parasitic transport of methanol (methanol crossover) severely impedes the performance of the direct methanol fuel cell (DMFC). 

The basic design of a fuel cell, an ionically conducting electrolyte and separator layer sandwiched between two electronically conducting gas diffusion electrodes (the fuel anode and the oxidant cathode, respectively), is shown schematically in Fig. 2 for a polymer electrolyte fuel cell with an acidic electrolyte and hydrogen and oxygen as the corresponding reactants. Typically, under open circuit conditions, H2/air fuel cells exhibit a cell voltage of... 

The application to fuel cells was reopened by Ballard stacks using a new Dow membrane that is characterized by short side chains. The extremely high power density of the polymer electrolyte fuel cell (PEFC) stacks was actiieved not only by the higher proton conductance of the membrane, but also by the usage of PFSA polymer dispersed solution, serpentine flow separators, the structure of the thin catalyst layer, and the gas diffusion layer. Although PFSA membranes remain the most commonly employed electrolyte up to now, their drawbacks, such as decrease in mechanical strength at elevated temperature and necessity for humidification to keep the proton conductance, caused the development of various types of new electrolytes and technologies [7], as shown in Fig. 2. 

Figure 18.1. Schematic of a single polymer electrolyte fuel cell, (1) bipolar plates (2) current collectors (3) gas-diffusion layers (4) catalytic layers (5) membrane.

Although in situ infrared spectroscopy has been applied widely in terms of the systems studied, the reflective electrodes employed have been predominantly polished metal or graphite, and so an important advance has been the study of electrochemical processes at more representative electrodes such as Pt/Ru on carbon [107,122,157], a carbon black/polyethylene composite employed in cathodic protection systems [158] and sol-gel Ti02 electrodes [159]. Recently, Fan and coworkers [160] took this concept one step further, and reported preliminary in situ FTIR data on the electro-oxidation of humidified methanol vapor at a Pt/Ru particulate electrode deposited directly onto the Nafion membrane of a solid polymer electrolyte fuel cell that was mounted within the sample holder of a diffuse reflectance attachment. As well as features attributable to methanol, a number of bands between 2200 and 1700 cm were observed in the spectra, taken under shortoperating conditions, the importance of which has already been clearly demonstrated [107]. 

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