Polymer electrolyte fuel cells conductivity

Polymer Electrolyte Fuel Cell. The electrolyte in a PEFC is an ion-exchange (qv) membrane, a fluorinated sulfonic acid polymer, which is a proton conductor (see Membrane technology). The only Hquid present in this fuel cell is the product water thus corrosion problems are minimal. Water management in the membrane is critical for efficient performance. The fuel cell must operate under conditions where the by-product water does not evaporate faster than it is produced because the membrane must be hydrated to maintain acceptable proton conductivity. Because of the limitation on the operating temperature, usually less than 120°C, H2-rich gas having Htde or no (

A membrane ionomer, in particular a polyelectrolyte with an inert backbone such as Nation . They require a plasticizer (typically water) to achieve good conductivity levels and are associated primarily, in their protonconducting form, with solid polymer-electrolyte fuel cells. 

P. J. S. Vie and S. Kjelstrup. Thermal conductivities from temperature profiles in the polymer electrolyte fuel cell. Electrochimica Acta 49 (2004) 1069-1077. 

Carbon-supported platinum (Pt) and platinum-rathenium (Pt-Ru) alloy are one of the most popular electrocatalysts in polymer electrolyte fuel cells (PEFC). Pt supported on electrically conducting carbons, preferably carbon black, is being increasingly used as an electrocatalyst in fuel cell applications (Parker et al., 2004). Carbon-supported Pt could be prepared at loadings as high as 70 wt.% without a noticeable increase of particle size. Unsupported and carbon-supported nanoparticle Pt-Ru, ,t m catalysts prepared using the surface reductive deposition... 

Later, Hinatsu et al. studied the uptake of water, from the liquid and vapor states at various temperatures, in acid form Nafion 117 and 125, and Aciplex and Flemion membranes, although the latter two similar products will not be discussed here. These studies were motivated by a concern over the deleterious effects, involving either overly dry or overly wet membranes, on electrical conductivity within the context of polymer electrolyte fuel cells and polymer electrolyte water electrolyzers. 

One of the most important parts of the fuel cell is the electrolyte. For polymer-electrolyte fuel cells this electrolyte is a single-ion-conducting membrane. Specifically, it is a proton-conducting membrane. Although various membranes have been examined experimentally, most models focus on Nafion. Furthermore. it is usually necessary only to modify property values and not governing equations if one desires to model other membranes. The models presented and the discussion below focus on Nafion. 

Nafion is a copolymer of poly(tetrafluoroethylene) and polysulfonyl fluoride vinyl ether. It has fixed anions, which are sulfonic acid sites, and consequently, by electroneutrality, the concentration of positive ions is fixed. Furthermore, the transference number of protons in this system is 1, which greatly simplifies the governing transport equations, as seen below. There can be different forms of Nafion in terms of the positive counterion (e.g., proton, sodium, etc.). Most models deal only with the proton or acid form of Nafion, which is the most common form used in polymer-electrolyte fuel cells due to its high proton conductivity. 

The purpose of the present review is to summarize the current status of fundamental models for fuel cell engineering and indicate where this burgeoning field is heading. By choice, this review is limited to hydrogen/air polymer electrolyte fuel cells (PEFCs), direct methanol fuel cells (DMFCs), and solid oxide fuel cells (SOFCs). Also, the review does not include microscopic, first-principle modeling of fuel cell materials, such as proton conducting membranes and catalyst surfaces. For good overviews of the latter fields, the reader can turn to Kreuer, Paddison, and Koper, for example. 

Figure 3.18 Schematic diagram of a polymer electrolyte fuel cell based on a proton-conductive...

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... 

Solid Polymer Electrolyte Fuel Cell Here, there is no apparent liquid solution, or high-temperature ionic conductor. The usual ionic solution between the electrodes is replaced by a well-humidified membrane made of a perfluorosulfonic acid polymer that conducts protons. 

Proton exchange membranes (PEM) fuel cells (or polymer electrolyte fuel cells - PEFCs), with H -conducting polymeric membranes, transports hydrogen (fuel) cations, generated at the anode, to an ambient air exposed cathode, where they are electro-oxidised to water at low temperatures. 

Ma Y,Wainright J, Savinell R, (2004). Conductivity of PBI Membranes for high-temperature polymer electrolyte fuel cells. Journal of Electrochemical Society, 151 8-16... 

Figure 5.16. Schematic illustration of a conductivity cell for Nafion membranes (1) graphite current collectors (2) carbon paper electrodes (3) membrane (4) electrical connections (5) beaker filled with deionized water and (6) thermocouple [15]. (Reprinted from Journal of Power Sources, 134, Silva RF, De Francesco M, Pozio A. Tangential and normal conductivities of Nafion membranes used in polymer electrolyte fuel cells, 18-26, 2004, with permission from Elsevier.)...

Silva RF, De Francesco M, Pozio A (2004) Tangential and normal conductivities of Nafion membranes used in polymer electrolyte fuel cells. JPower Sources 134 18-26... 

Fig. 23. Schematic illustrations for solid polymer electrolyte fuel cell and composite electrode with Pt catalyst, carbon conducting material, and binding polymer material.

The idea of using an ion-conductive polymeric membrane as a gas-electron barrier in a fuel cell was first conceived by William T. Grubb, Jr. (General Electric Company) in 1955. - In his classic patent, Grubb described the use of Amber-plex C-1, a cation exchange polymer membrane from Rohm and Haas, to build a prototype H2-air PEM fuel cell (known in those days as a solid-polymer electrolyte fuel cell). Today, the most widely used membrane electrolyte is DuPont s Nation... 

Silva, R.R et al., Surface conductivity and stability of metallic bipolar plate materials for polymer electrolyte fuel cells, Electrochim. Acta, 51, 3592, 2006. 

Polymer-electrolyte fuel cells (PEFC and DMFC) possess a exceptionally diverse range of applications, since they exhibit high thermodynamic efficiency, low emission levels, relative ease of implementation into existing infrastructures and variability in system size and layout. Their key components are a proton-conducting polymer-electrolyte membrane (PEM) and two composite electrodes backed up by electronically conducting porous transport layers and flow fields, as shown schematically in Fig. 1(a). 

Kolde, J.A. Bahar, B. Wilson, M.S. Zawod-zinski, T.A. Gottesfeld, S. Advanced composite polymer electrolyte fuel cell membranes. In Proton Conducting Membrane Fuel Cells / The Electrochemical Society Chicago, IL, 1995. 

The development of new polymeric materials for polymer electrolyte fuel cell is one of the most active research areas, aiming at the new energy sources for electric cars and other devices. The mainstream of the material research for fuel cell is perfluoroalkyl sulfonic acid membranes such as Nafion, Acipex, and Flemion. The most well-known one is Nafion of Du Pont, which is derived from copolymers of tetrafluoro-ethylene and perfluorovinyl ether terminated by a sulfonic acid group.Protons, when dissociated from the sulfonic acid groups in aqueous environment, become mobile and the membrane becomes a proton conducting electrolyte membrane. 

G. Halpert, A. Landgrebe, Eds., Proc. First Int. Symp. on Proton Conducting Membrane Fuel Cells, The Electrochemical Society Proceedings, Advanced Composite Polymer Electrolyte Fuel Cell Membranes, Vol. 95-23, 1995, 193-201... 

Ostrovskii and coworkers have also reported the application of PVDF-SPS proton conducting materials in Hj/Og polymer electrolyte fuel cells (PEFC). Proton conductivities as high as 0.13 S cm at room temperature were measured. The PVDF-SPS materials were fabricated by electron irradiation followed by grafting and sulfonation. It is well known that y rays, electrons, or... 

Bio-inspired membranes for advanced polymer electrolyte fuel cells (anhydrous proton-conducting membrane via molecular self-... 

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. 

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