Polymer Electrolyte Membrane PEM

PEM fuel cells operate at relatively low temperatures, around 80°C. Low temperature operation allows them to start quickly (less warm-up time) and results in less wear on system components, resulting in better durability. However, they require that a noble-metal catalyst (typically platinum) be used to separate the hydrogen s electrons and protons, adding to system cost. The platinum catalyst is also extremely sensitive to CO poisoning, making it necessary to employ an additional reactor to reduce CO in the fuel gas if the hydrogen is derived from an alcohol or hydrocarbon fuel. This also adds cost. Developers are currently exploring platinum/ruthenium catalysts that are more resistant to CO. 

PEM fuel cells are used primarily for transportation applications and some stationary applications. Due to their fast start-up time, low sensitivity to orientation, and favourable power-to-weight ratio, PEM fuel cells are particularly suitable for use in passenger vehicles, such as cars and buses. 

PEM fuel cells have emerged as the most common type of fuel cell under development today. As stated above, they also are commonly referred to as proton exchange membrane fuel cells based on the key characteristic of the solid electrolyte membrane to transfer protons from the anode to the cathode. The solid electrolyte avoids problems caused by liquid electrolytes used in other systems, and the temperature range of 100°C enables rapid start-up under low temperature operation, with operation possible down to subfreezing temperatures. The lower temperature also allows a wider range of materials to be used and enables relatively easy stack design in terms of sealing issues and material selection. This type of fuel cell is the most feasible for use under transportation applications. 

The highly acidic membrane necessitates the use of very stable highly reactive catalysts, with platinum (Pt) being the only one in use today sufficiently active to achieve required performances. The fuel used can either be pure hydrogen 

Solid organic polymer polyper-fluorsulfonic acid 

Aqueous solution of potassium hydroxide soaked in a matrix 

Solid Oxide Yttria stabilized 600-1000°C lkW-3 35M3% 90% Auxiliary High efficiency 

Advantages of PEM-based RFC systems compared with alkaline RFCs are 

The challenges are to reduce the costs and to improve the durability [17, pp. 271-289]. RFCs have a separate electrolysis and FC module or are constracted as URFCs where both reactions take place in the same cell. A brief overview of the electrodes for separate electrolyzer and FC is given first, followed by a more detailed description of the bifunctional electrodes for URFCs. 

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The concept of a promoter can also be extended to the case of substances which enhance the performance of an electrocatalyst by accelerating the rate of an electrocatalytic reaction. This can be quite important for the performance, e.g., of low temperature (polymer electrolyte membrane, PEM) fuel cells where poisoning of the anodic Pt electrocatalyst (reaction 1.7) by trace amounts of strongly adsorbed CO poses a serious problem. Such a promoter which when added to the Pt electrocatalyst would accelerate the desired reaction (1.5 or 1.7) could be termed an electrocatalytic promoter, or electropromoter, but this concept will not be dealt with in the present book, where the term promoter will always be used for substances which enhance the performance of a catalyst. 

Figure 8.31. Principle of a Polymer Electrolyte Membrane (PEM) fuel cell. A Nation membrane sandwiched between electrodes separates hydrogen and oxygen. Hydrogen is oxidized into protons and electrons at the anode on the left. Electrons flow through the outer circuit, while protons diffuse through the...

In addition to these smaller applications, fuel cells can be used in portable generators, such as those used to provide electricity for portable equipment. Thousands of portable fuel cell systems have been developed and operated worldwide, ranging from 1 watt to 1.5 kilowatts in power. The two primary technologies for portable applications are polymer electrolyte membrane (PEM) and direct methanol fuel cell (DMFC) designs. 

Thousands of smaller stationary fuel cells of less than 10 kilowatts each have been built and operated to power homes and provide backup power. Polymer electrolyte membrane (PEM) fuel cells fueled with natural gas or hydrogen are the primary units for these smaller systems. 

The DOD has also begun a residential fuel cell demonstration program using polymer electrolyte membrane (PEM) fuel cells ranging in size from 1 to 20 kilowatts. This will include twenty-one PEM fuel cells at nine U.S. military bases. The first units were installed in 2002. 

One of the applications for hydrogen is for Polymer Electrolyte Membrane (PEM) fuel cells. As mentioned earlier, one application is a hydrogen fuelled hybrid fuel cell / ultra-capacitor transit bus program where significant energy efficiencies can be demonstrated. Another commercial application is for fuel cell powered forklifts and other such fleet applications that requires mobile electrical power with the additional environmental benefits this system provides. Other commercial applications being developed by Canadian industry is for remote back-up power such as the telecommunications industry and for portable fuel cell systems. 

Under normal operation of an H2/O2 fuel cell, anodic oxidation of IT2 (or other hydrocarbons or alcoholic fuels)—that is, H2 —> 2H+ -1- 2e —produces protons that move through the polymer electrolyte membrane (PEM) to the cathode, where reduction of O2 (i.e., O2 -1- 2H+ -1- 2e —> H2O) produces water. The overall redox process is H2 -1-O2 —> H2O. The electronically insulating PEM forces electrons produced at the anode through an external electric circuit to the cathode to perform work in stationary power units, drive trains... 

A fuel cell that has desirable features for transportation and portable power is the polymer electrolyte membrane (PEM) system. The core of this technology is a polymer membrane that conducts... 

Figure 26. Schematic of a polymer electrolyte membrane (PEM) fuel cell. The fuel cell stacks operate at 30—180 °C with 30—60% efficiency. Fuel options include pure hydrogen, methanol, natural gas, and gasoline.

By 2010, develop and demonstrate technology to supply purified hydrogen (purity sufficient for polymer electrolyte membrane (PEM) fuel cells) from biomass at 2.60/kg at the plant gate (projected to a commercial scale 75,000 kg/day). The objective is to be competitive with gasoline by 2015. 

In PEMFC systems, water is transported in both transversal and lateral direction in the cells. A polymer electrolyte membrane (PEM) separates the anode and the cathode compartments, however water is inherently transported between these two electrodes by absorption, desorption and diffusion of water in the membrane.5,6 In operational fuel cells, water is also transported by an electro-osmotic effect and thus transversal water content distribution in the membrane is determined as a result of coupled water transport processes including diffusion, electro-osmosis, pressure-driven convection and interfacial mass transfer. To establish water management method in PEMFCs, it is strongly needed to obtain fundamental understandings on water transport in the cells. 

Detected MRI signal should be converted for water content in a polymer electrolyte membrane (PEM). Our group performed a simple approach to relate the image intensity to the water content in the membrane by acquiring a series of MR images of an MEA exposed to water vapor activity, a, that are known to result in specific values of X, as the following equation found in literature.40... 

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... 

Polymer Electrolyte Membrane (PEM) fuel cell bipolar plates, discussion of the difficulties associated with confronting bipolar plate development... 

The hybrid sulphur (HyS) cycle utilises the same H2S04 decomposer and acid concentration section as the S-I plant. The S02 electrolysers are polymer electrolyte membrane (PEM) technology. The hydrogen plant is coupled to two NHSS and produces 4.0 kg/s of product. Oxygen is sold as a by-product. The Rankine bottoming cycle generates 133 MWe for the electrolysis section and an additional 198 MWe is imported. 

Some of the common electrolysers are Alkaline Electrolysers, Polymer Electrolyte Membrane (PEM) Electrolysers (also known as Proton Exchange Membrane electrolysers), and Steam Electrolysers. In alkaline electrolysers a liquid electrolyte, such as a 25% potassium hydroxide solution, is used. At... 

In Figure 1 the circuit of functional units traditional oxygen-hydrogen FC with clamping contacts)) is shown. Symmetrically on both sides of the polymer electrolyte membrane (PEM) (a position 1) the units included in anode and cathode electrodes are represented (positions 2-5, for simplicity units are numbered only on the one hand). 

Fuel cells are the primary technology that will advance hydrogen use (DOE, 1998). Fuel cells are important as they are one component of a system that can efficiently produce electricity for many applications (Jacoby, 1999). It is also widely accepted that fuel cells are environmentally friendly (Hirschenhofer, 1997). Low temperature fuel cells, such as polymer-electrolyte-membrane (PEM) fuel cells, are being considered for many applications including electric power generation in commercial and residential buildings, automobile applications and... 

Figure 3.5. Process diagram of alkaline electrolysis for the production of H2 Polymer Electrolyte Membrane (PEM) Electrolysis...

Polymer-electrolyte membrane (PEM) Sulfuric acid impregnated in membrane 60-80... 

A second commercially available electrolyzer technology is the solid polymer electrolyte membrane (PEM). PEM electrolysis (PEME) is also referred to as solid polymer electrolyte (SPE) or polymer electrolyte membrane (also, PEM), but all represent a system that incorporates a solid proton-conducting membrane which is not electrically conductive. The membrane serves a dual purpose, as the gas separation device and ion (proton) conductor. High-purity deionized (DI) water is required in PEM-based electrolysis, and PEM electrolyzer manufacturer regularly recommend a minimum of 1 MQ-cm resistive water to extend stack life. 

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