Polymer electrolyte fuel cells Hydrogen PEFCs

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... 

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. 

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... 

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. 

The conversion of hydrocarbon to hydrogen will play an important role in 21st century, especially, for providing hydrogen for polymer electrolyte fuel cell (PEFC). Currently, steam reforming of hydrocarbons, especially of CH4 (1), is the largest and generally the most economical way to make Hz. Alternative industrial chemical approach includes CH4 + HzO = CO H- 3Hz (1)... 

Hydrogen in the gaseous state has long been investigated as a clean energy source for internal combustion engines and PEMFC. [Note PEMFC is sometimes simply called Polymer Electrolyte Fuel Cell (PEFC)]. 

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). 

Kato H (2007) Current status and future perspective of MEA development for PEFC, 3rd international hydrogen and fuel cell expo, FC EXPO 2007, FC-8, the most-developed element technology of polymer electrolyte fuel cells, Tokyo, pp 45-72... 

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