Polymer Electrolyte Fuel Cell PEFC

Polymer electrolyte fuel cells (PEFCs) have attracted great interest as a primary power source for electric vehicles or residential co-generation systems. However, both the anode and cathode of PEFCs usually require platinum or its alloys as the catalyst, which have high activity at low operating temperatures (<100 °C). For large-scale commercialization, it is very important to reduce the amount of Pt used in fuel cells for reasons of cost and limited supply. 

Carbon is unique among chemical elements since it exists in different forms and microtextures transforming it into a very attractive material that is widely used in a broad range of electrochemical applications. Carbon exists in various allotropic forms due to its valency, with the most well-known being carbon black, diamond, fullerenes, graphene and carbon nanotubes. This review is divided into four sections. In the first two sections the structure, electronic and electrochemical properties of carbon are presented along with their applications. The last two sections deal with the use of carbon in polymer electrolyte fuel cells (PEFCs) as catalyst support and oxygen reduction reaction (ORR) electrocatalyst. 

Polymer Electrolyte Fuel Cell (PEFC) The electrolyte in this fuel cell is an ion exchange membrane (fluorinated sulfonic acid polymer or other similar polymer) that is an excellent proton conductor. The only liquid in this fuel cell is 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 byproduct water does not evaporate faster than it is produced because the membrane must be hydrated. Because of the limitation on the operating... 

Recently, the major activity in transportation fuel cell development has focused on the polymer electrolyte fuel cell (PEFC). In 1993, Ballard Power Systems (Burnaby, British Columbia, Canada) demonstrated a 10 m (32 foot) light-duty transit bus with a 120 kW fuel cell system, followed by a 200 kW, 12 meter (40 foot) heavy-duty transit bus in 1995 (26). These buses use no traction batteries. They operate on compressed hydrogen as the on-board fuel. In 1997, Ballard provided 205 kW (275 HP) PEFC units for a small fleet of hydrogen-fueled, full-size transit buses for demonstrations in Chicago, Illinois, and Vancouver, British Columbia. Working... 

Polymer electrolyte fuel cells (PEFC) deliver high power density, which offers low weight, cost, and volume. The immobilized electrolyte membrane simplifies sealing in the production process, reduces corrosion, and provides for longer cell and stack life. PEFCs operate at low temperature, allowing for faster startups and immediate response to changes in the demand for power. The PEFC system is seen as the system of choice for vehicular power applications, but is also being developed for smaller scale stationary power. For more detailed technical information, there are excellent overviews of the PEFC (1,2). 

Bolwin, K., Giilzow, E., Bevers, D., and Schnurnberger, W. Preparation of porous electrodes and laminated electrode-membrane structures for polymer electrolyte fuel cells (PEFCs). Solid State Ionics 1995 77 324-330. 

Savadogo, O. 2004. Emerging membranes for electrochemical systems—Part 11. High-temperature composite membranes for polymer electrolyte fuel cell (PEFC) applications. Journal of Power Sources 127 135-161. 

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. 

The polymer electrolyte fuel cell (PEFC) or proton exchange membrane fuel cell—also known as the polymer electrolyte membrane fuel cell (PEMFC)—is a lower temperature fuel cell (typically less than 100°C) with a special polymer electrolyte membrane. This lower temperature fuel cell is well suited for transportation, portable, and micro fuel cell applications because of the importance of fast start-up and dynamic operation. The PEMFC has applicability in most market and application areas. 

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... 

Proton exchange membrane fuel cells (PEMFCs) work with a polymer electrolyte in the form of a thin, permeable sheet. The PEMFCs, otherwise known as polymer electrolyte fuel cells (PEFC), are of particular importance for the use in mobile and small/medium-sized stationary applications (Pehnt, 2001). The PEM fuel cells are considered to be the most promising fuel cell for power generation (Kazim, 2000). 

The DMFC, based on a polymer electrolyte fuel cell (PEFC), uses methanol directly for electric power generation and promises technical advantages for power trains. The fuel can be delivered to the fuel cell in a gaseous or liquid form. The actual power densities of a DMFC are clearly lower than those of a conventional hydrogen-fed polymer electrolyte fuel cell. In addition, methanol permeates through the electrolyte and oxidizes at the cathode. This results in a mixed potential at the cathode (Hohlein et al., 2000). 

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. 

Table 2. Comparisons of Representative CFD Models for Polymer Electrolyte Fuel Cells (PEFCs)...

One particular application for which supported Au catalysts may find a niche market is in fuel cells [4, 50] and in particular in polymer electrolyte fuel cells (PEFC), which are used in residential electric power and electric vehicles and operate at about 353-473 K. Polymer electrolyte fuel cells are usually operated by hydrogen produced from methane or methanol by steam reforming followed by water-gas shift reaction. Residual CO (about 1 vol.%) in the reformer output after the shift reaction poisons the Pt anode at a relatively low PEFC operating temperature. To solve this problem, the anode of the fuel cell should be improved to become more CO tolerant (Pt-Ru alloying) and secondly catalytic systems should be developed that can remove even trace amounts of CO from H2 in the presence of excess C02 and water. 

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 8.3 shows a schematic representation of a polymer electrolyte fuel cell (PEFC). In this instance, the oxidation reaction in the cathode is given by... 

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. 

Similarly, the phosphoric acid fuel cell (PAFC), although still selling, is resisting efforts to get its capital costs down to the level at which it could be mass produced, and hence another chapter is eliminated. Reference is, however, made to the part played by the PAEC in evolving the catalysts for the polymer electrolyte fuel cell (PEFC). 

Ballard Power Systems of Canada (see web site) is the Titan, the co-ordinating major force in the international proton exchange fuel cell or polymer electrolyte fuel cell (PEFC) business. Ballard claims over 500 patents Also, a worldwide complex of allies serves its international interests. 

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