Polymer electrolyte fuel cell catalyst layers

Direct simulation of polymer electrolyte fuel cell catalyst layers, presentation of a systematic development of the direct numerical simulation... 

P. P. Mukheijee, Pore-scale modeling and analysis of the polymer electrolyte fuel cell catalyst layer , Ph.D. Dissertation, The Pennsylvania State University, USA (2007). 

Wilson, M. S. and Gottesfeld, S., Thin film catalyst layers for polymer electrolyte fuel cell electrodes, J. Appl. Electrochem., 22, 1, 1992. 

Xie, Z., Navessin, T, Shi, K., Chow, R., Wang, Q., Song, D., Andreaus, B., Eikerling, M., Liu, Z., and Holdcroft, S. Eunctionally graded cathode catalyst layers for polymer electrolyte fuel cells. Journal of the Electrochemical Society 2005 152 A1171-A1179. 

Cheng, X., Yi, B., Han, M., Zhang, J., Qiao, Y., and Yu, J. Investigation of platinum utilization and morphology in catalyst layer of polymer electrolyte fuel cells. Journal of Power Sources 1999 79 75-81. 

Wang, G., Mukherjee, P P, and Wang, C. Y. Optimization of polymer electrolyte fuel cell cathode catalyst layers via direct numerical simulation modeling. Electrochimica Acta 2007 52 6367-6377. 

Passalacqua, E., Lufrano, F., Squadrito, G., Patti, A., and Giorgi, L. Nafion content in the catalyst layer of polymer electrolyte fuel cells Effects on structure and performance. Electrochimica Acta 2001 46 799-805. 

Figure 13.9 Schematic diagram of a polymer electrolyte fuel cell (A) gas manifolding, (B) porous graphite block, (C) active catalyst layer (dispersed Pt and Teflon binder), and (D) polymer electrolyte.

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... 

M. Eikerling and A. Komyshev, Modeling the performance of the cathode catalyst layer of polymer electrolyte fuel cells, J. Electroanal. Chem. 435 (1998) 98-106. 

Figure 5.30. Schematic of the catalyst layer geometry and its composition, exhibiting the different functional parts, a A sketch of the layer, used to construct a continuous model, b A one-dimensional transmission-line equivalent circuit where the elementary unit with protonic resistivity Rp, the charge transfer resistivity Rch and the double-layer capacitance Cj are highlighted [34], (Reprinted from Journal of Electroanalytical Chemistry, 475, Eikerling M, Komyshev AA. Electrochemical impedance of the cathode catalyst layer in polymer electrolyte fuel cells, 107-23, 1999, with permission from Elsevier.)...

Eikerling M, Komyshev AA (1999) Electrochemical impedance of the cathode catalyst layer in polymer electrolyte fuel cells. J Electroanal Chem 475 107-23... 

Figure 6.8. Polarization curves of fuel cells with electrodes made of catalyst layers containing various amounts of Nation ( ) 0.2 ( ) 0.8 (A) 2.0 mg/cm2 [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.)...

Wilson, M.S. and Gottesfeld, S., High performance catalyzed membranes of ultra-low Pt loadings for polymer electrolyte fuel cells, J. Electrochem. Soc., 139, L28, 1992. Wilson, M.S. and Gottesfeld, S., Thin-fihn catalyst layers for polymer electrolyte fuel cell electrodes, J. Appl. Electrochem., 22, 1, 1992. 

Xie, Z. et ah. Functionally graded cathode catalyst layers for polymer electrolyte fuel cells, J. Electrochem. Soc., 152, A1171, 2005. 

Figure 3.52. Efficiency of a reversible PEM fuel cell as a function of the amount (at. % or mol %) of Ir in the form of IrOj relative to Pt in the positive electrode catalyst, for fuel cell electricity production (EC) or for water electrolysis (WE). Also the product of the two efficiencies relevant for storage cycles is shown. The catalyst is otherwise similar to that of Fig. 3.51, with PTFE and Nation channels. (From T. loroi, K. Ya-suda, Z. Siroma, N. Fujiwara, Y. Miyazaki (2002). Thin film electrocatalyst layer for unitized regenerative polymer electrolyte fuel cell. J. Power Sources 112, 583-587. Used by permission from Elsevier. See also loroi et al. (2004).

We will describe in this section the variety of techniques for the preparation of catalyst layers in polymer electrolyte fuel cells, in chronological order of development. 

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... 

F. Uribe and T. Zawodzinski, "A Study of Polymer Electrolyte Fuel Cell Performance at High Voltages. Dependence on Cathode Catalyst Layer Composition and on Voltage Conditioning". Accepted in Electrochimica Acta. (2002). 

The membrane is the heart of the fuel-cell sandwich and hence the entire fuel cell. It is this electrolyte that makes polymer-electrolyte fuel cells (PEFCs) unique and, correspondingly, the electrolyte must have very specific properties. Thus, it needs to conduct protons but not electrons as well as inhibit gas transport in the separator but allow it in the catalyst layers. Furthermore, the membrane is one of the most important items in dealing with water management. It is for these reasons as well as for others that modeling and experiments of the membrane have been pursued more than any other layer [1],... 

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. 

A. A. Kulikovsky. Performance of catalyst layers of polymer electrolyte fuel cells Exact solutions. Electrochem. Comm., 4(4) 318-323, 2002. 

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. 

Wannek C, Lehnert W, Mergel J (2009) Membrane electrode assemblies for high-temperature polymer electrolyte fuel cells based on poly (2,5-benzimidazole) membranes with phosphoric acid impregnation via the catalyst layer. J Power Sources 192 258-266... 

Soboleva T, Zhao X, Malek K, Xie Z, Navessin T, Holdcroft S (2010) On the micro-, meso-, and macroporous structures of polymer electrolyte membrane fuel cell catalyst layers. ACS Appl Mater Interfaces 2 375-384... 

Uchida M, Fukuoka Y, Sugawara Y, Eda N, Ohta A (1996) Effects of microstructure of carbon support in the catalyst layer on the performance of polymer-electrolyte fuel cells. J Electrochem Soc 143 2245-2252... 

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