PEM fuel cells gas diffusion layer

K. T. Jeng, S. E. Lee, G. E. Tsai, and C. H. Wang. Oxygen mass transfer in PEM fuel cell gas diffusion layers. Journal of Power Sources 138 (2004) 41-50. 

Lim, C. Wang, C. Y. Measurement of contact angles of liquid water in PEM fuel cell gas diffusion layer (GDL) by sessile drop and capillary rise methods. Penn State University Electrochemical Engine Center (ECEC) Technical Report no. 2001 03, Perm State University State College, PA, 2001. 

Sadeghi, E., Djilali, N., and Bahrami, M. 2008. Analytic determination of the effective thermal conductivity of PEM fuel cell gas diffusion layers. 1 200-208. 

S. Litster, D. Sinton, and N. DjUah, Ex situ Visualization Liquid Water Transport in PEM Fuel Cell Gas Diffusion Layers, /. Power Sources, Vol. 154, pp. 95-105, 2006. 

C. Boyer, S. Gamhurzev, O. Velev, S. Srinivasan, and A.J. Appleby. Measurements of proton conductivity in the active layer of PEM fuel cell gas diffusion electrodes. Electrochimica Acta 43, 3703-3709 1998. 

To understand the modifications made to polysaccharides in PEMs applications, a cursory knowledge of fuel cells is necessary. A fuel cell is an electrochemical cell that converts chemical fuel into electrical energy. Figure 3.4 shows a simplified view of a proton conductive fuel cell. The main components in a PEM fuel cell are catalyst layers, gas diffusion layers and the PEM itself. These three components comprise the membrane electrode assembly. The catalyst... 

The main components of a PEM fuel cell are the flow channels, gas diffusion layers, catalyst layers, and the electrolyte membrane. The respective electrodes are attached on opposing sides of the electrolyte membrane. Both electrodes are covered with diffusion layers, and the flow channels/current collectors. The flow channels collect current from the electrodes while providing the fuel or oxidant with access to the electrodes. The gas diffusion layer allows gases to diffuse to the electro-catalysts and provides electrical contact throughout the catalyst layers. Within the anode catalyst layer, the fuel (typically H2) is oxidized to produce electrons and protons. The electrons travel through an external circuit to produce electricity, while the protons pass through the proton conducting electrolyte membrane. Within the cathode catalyst layer, the electrons and protons recombine with the oxidant (usually 02) to produce water. 

An analysis of the individual PEM components offers evidence of almost unbroken R D see Fig. 13.10 (Jochem et al., 2007). The overall importance of the membrane is striking. Furthermore, the numbers of annual applications for bipolar plates (BPP) and the gas-diffusion layer (GDL) decrease after 2002, while the increase in membrane applications flattens out. This correlates with the equally lower number of fuel cell patents in the field of mobile applications. 

Figure 2.1 shows a schematic structure of the fuel cell membrane electrode assembly (MEA), including both anode and cathode sides. Each side includes a catalyst layer and a gas diffusion layer. Between the two sides is a proton exchange membrane (PEM) conducting protons from the anode to the cathode. 

Antoine et al. [28] inveshgated the gradient across the CL and found that the Pt utilization was dependent on the CL porosity. In a nonporous CL, catalyst utilization was increased through the preferential locahon of Pt close to the gas diffusion layer in a porous CL, catalyst utilization efficiency was increased through the preferential location of Pt close to the polymer electrolyte membrane. In PEM fuel cells, fhe CL has a porous structure, and better performance is expected if higher Pf loading is used af preferential locahons close to the membrane/catalyst layer interface. 

Besides silicon, other materials have also been used in micro fuel cells. Cha et al. [79] made micro-FF channels on SU8 sheets—a photosensitive polymer that is flexible, easy to fabricate, thin, and cheaper than silicon wafers. On top of fhe flow channels, for both the anode and cathode, a paste of carbon black and PTFE is deposited in order to form the actual diffusion layers of the fuel cell. Mifrovski, Elliott, and Nuzzo [80] used a gas-permeable elastomer, such as poly(dimethylsiloxane) (PDMS), as a diffusion layer (with platinum electrodes embedded in it) for liquid-electrolyte-based micro-PEM fuel cells. 

F. Y. Zhang, S. G. Advani, and A. K. Prasad. Performance of a metallic gas diffusion layer for PEM fuel cells. Journal of Power Sources 176 (2008) 293-298. 

M. S. Yazici and D. Krassowski. Development of a unique, expanded graphite gas diffusion layer for PEM fuel cells. Fuel Cell Seminar Proceeding Fuel Cell Progress, Challenges and Markets. Fuel Cell Seminar Palm Springs CA, Nov. 14-18 (2005), 117-120. 

K. Jiao and B. Zhou, hmovative gas diffusion layers and their water removal characteristics in PEM fuel cell cathode. Journal of Power Sources 169 (2007) 296-314. 

M. V. Williams, H. R. Kunz, and J. M. Fenton. Operation of Nafion(R)-based PEM fuel cells with no external humidification Influence of operating conditions and gas diffusion layers. Journal of Power Sources 135 (2004) 122-134. 

J. H. Jang, W. M. Yan, and G. G. Shih. Effects of the gas diffusion-layer parameters on cell performance of PEM fuel cells. Journal of Power Sources 161 (2006) 323-332. 

O. Ghapuis, M. Prat, M. Quintard, et al. Two-phase flow and evaporation in model fibrous media Application to the gas diffusion layer of PEM fuel cells. Journal of Power Sources 178 (2008) 258-268. 

J. Benziger, J. Nehlsen, D. Blackwell, T. Brennan, and J. Itescu. Water flow in the gas diffusion layer of PEM fuel cells. Journal of Membrane Science 261 (2005) 98-106. 

I. Nitta, O. Himanen, and M. Mikkola. Thermal conductivity and contact resistance of compressed gas diffusion layer of PEM fuel cell. Fuel Cells 8 (2008) 111-119. 

J. Park and X. Li. An experimental and numerical investigation on the cross flow through gas diffusion layer in a PEM fuel cell with a serpentine flow channel. Journal of Power Sources 163 (2007) 853-863. 

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 12.1 is a schematic view of a typical PEM fuel cell. A membrane electrode assembly (MEA) usually refers to a five-layer structure that includes an anode gas diffusion layer (GDL), an anode electrode layer, a membrane electrolyte, a cathode electrode layer, and a cathode GDL. Most recently, several MEA manufacturers started to include a set of membrane subgaskets as a part of their MEA packages. This is often referred to as a seven-layer MEA. In addition to acting as a gas and... 

Proton exchange membrane (PEM) fuel cells are the primary choice for transportation systems, but they can also be useful for stationary power production or local hydrogen production. Most of the challenges of PEM fuel cell commercialization center around cost and materials performance in an integrated system. Some specific issues are the cost of catalyst materials, electrolyte performance, i.e., transport rates, and water collection in the gas diffusion layer (GDL). 

Figure 3.32. Layout of a PEM fuel cell layer, several of which may be stacked. Electrode areas include gas diffusion and electrode components in a grid-type structure (cf. Fig. 3.33) (from B. Sorensen, Renewable Energy, 2004, used by permission from Elsevier).

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.)...

Figure 3.41. Structure of carbon paper (left) and carbon cloth (right) used for gas diffusion layers in PEM fuel cells. A coating of 20% (by weight) fluorinated ethylene propylene has been applied. (From C. Lim and C-Y. Wang (2004). Effects of hydro-phobic polymer content in GDL on power performance of a PEM fuel cell. Electro chimica Acta 49, 4149-4156 G. Lu and C-Y. Wang (2004). Electrochemical and flow characterization of a direct methanol fuel cell.. Power Sources 134, 33-40. Used with permission from Elsevier.)...

The theoretical power density of a DMFC at 0.5 V is about 1600 Wh per kg of methanol fuel, but in practice, small DMFCs for portable applications have achieved much less. If small DMFCs are designed like conventional PEM cells, including a membrane-electrode assembly (MEA), two gas diffusion layers, fuel and air channels with forced flows and current collectors, they may achieve power densities of about 0.015-0.050 W cm at temperatures in the range of 23-60°C (Lu et al., 2004), consistent with the value found at 85°C in Fig. 3.53. 

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