Fuel cell requirements

Considerable research has been carried out in the field of fuel processing and reviews of some of the key technologies are readily available (Dicks, 1996). The following sections are intended to provide a basic explanation of the various technologies. Some detailed design of individual reactors and systems are proprietary, of course, but there is a wealth of information also available from various organisations involved in the development 

Gas species PEM fuel cell AFC PAFC MCFC SOFC 

Natural gas and petroleum liquids contain organic sulphur compounds that normally have to be removed before any further fuel processing can be carried out. Even if suphur levels in fuels are below 0.2 ppm, some deactivation of steam reforming catalysts can occur. Shift catalysts are even more intolerant to sulphur (Farrauto, 2001), and to ensure adequate lifetimes of fuel processors the desulphurisation step is very important. Even if the fuel processor catalysts were tolerant to some sulphur, it has been shown that levels of only 1 ppb are enough to permanently poison a PEM anode catalyst. 

The sulphur compounds found in fuels vary. In the case of natural gas, the only sulphur compounds may be the odorants that have been added by the utility company for safely reasons. With petroleum fractions, the compounds may be highly aromatic in nature. Gasoline currently contains some 300 to 400 ppm of sulphur as organic compounds. In the drive to reduce emissions from vehicles, regulations are being introduced to limit the sulphur in gasoline and diesel fuels. For example in the United States, the proposed limit is 30 to 80 ppm for the year 2004. As levels are reduced, the methods used to remove or desulphurise such fuels may need to be adapted. 

For these reasons the design of a desulphurisation system must be undertaken with care. If the fuel cell plant has a source of hydrogen-rich gas (usually from the reformer exit), it is common practice to recycle a small amount of this back to a hydrodesulphurisation (HDS) reactor. In this reactor, any organic sulphur-containing compounds are converted, over a supported nickel-molybdenum oxide or cobalt-molybdenum oxide catalyst, into hydrogen sulphide via hydrogenolysis reactions of the type 

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The catalyst layer is the most expensive part of this fuel cell. It is made from a mixture of platinum, carbon powder, and PEM powder, bonded to a conductive carbon fiber cloth. We obtained ours from E-Tek Inc. The cost for an order of their ELAT catalyst cloth sheet includes a setup charge. So get together with others for a larger order if you want to keep costs down. We paid 360 for a piece of ELAT 15.2 centimeters by 15.2 centimeters [6 inches by 6 inches] including the 150 setup charge. This piece provides enough for about twelve disks. Each fuel cell requires two disks of ELAT and one larger disk of PEM to make the sandwich, so you can make six cells from this size... 

Hydrocarbons such as natural gas or methane can be reformed internally in the SOFC, which means that these fuels can be fed to the cells directly. Other types of fuel cells require external reforming. The reforming equipment is size-dependent which reduces the modularity. 

Fuel processing is defined in this Handbook as the conversion of a commercially available gas, liquid, or solid fuel (raw fuel) to a fuel gas reformate suitable for the fuel cell anode reaction. Fuel processing encompasses the cleaning and removal of harmful species in the raw fuel, the conversion of the raw fuel to the fuel gas reformate, and downstream processing to alter the fuel gas reformate according to specific fuel cell requirements. Examples of these processes are ... 

CO content to the fuel cell requirement and additional shifting and alteration will be needed for lower temperature fuel cells. 

The installation of fuel stationary fuel cells requires adherence to a variety of building codes. A few of the major codes are summarized below. 

Electrocatalysis in fuel cells requires as well substances capable of catalyzing the anodic oxidation of fuels as catalysts for the cathodic reduction of oxygen. Several dyestuffs that catalyze oxygen reduction are known, but up to now only one has been described as active in anodic reactions. All these dyestuffs are N4-chelates. 

Research Focus Synthesis of sulfamic acid electrolytic polymers for fuel cells requiring high proton conductivity and open circuit voltages. 

Amazingly, a car powered by a hydrogen-oxygen fuel cell requires only about 3 kilograms of hydrogen to travel 500 kilometers. However, this much hydrogen gas at room temperature and atmospheric pressure would occupy a volume of about 36,000 liters, the volume of about four midsize cars Thus the major hurdle to the development of fuel-cell technology lies not with the cell, but with the fuel. This volume of gas could be compressed to a much smaller volume, as it is on the experimental buses in Vancouver. 

Fuel cells require a steady supply of hydrogen. Therein lies the biggest problem in promoting the widespread use of fuel cells how to create, transport and store the hydrogen. At present, no one has been able to put a viable plan in place that would create a network of hydrogen fueling stations substantial enough to meet the needs of everyday motorists in the U.S. or anywhere else. 

For many potential applications a fuel cell system must be capable of surviving and operating in extreme conditions. Presence of water in the membrane and fuel cell requires special attention to fuel cell stack and system design to allow system survival and start-up in extremely cold conditions. Most automotive systems have already demonstrated this capability. 

In microbial fuel cells living microorganisms serve as bio catalysts for the conversion of chemical energy to electricity. Since the majority of microorganisms are electrochemically inactive some early microbial fuel cells required the use of artificial electron-shuttling com-... 

Molten carbonate fuel cell technology was developed based on the work of Bauers and Ehrenberg, Davy tan, and Broers and Ketelaar in the 1940s [8], The electrolyte is a molten salt such as sodium carbonate, borax, or cryolite. This type of fuel cell requires a high temperature to keep the electrolyte in a molten state. The following 30-40 years saw great successes, with the development of MCFCs and MCFC stacks that could be operated for over 5000 hours. 

Fuel cells, due to their higher efficiency in the conversion of chemical into electrical energy vhth respect to thermo-mechanical cycles, are another major area of R D that has emerged in the last decade. Their effective use, ho vever, still requires an intense effort to develop ne v materials and catalysts. Many relevant contributions from catalysis (increase in efficiency of the chemical to electrical energy conversion and the stability of operations, reduce costs of electrocatalysts) are necessary to make a step for vard in the application of fuel cells out of niche areas. This objective also requires the development of efficient fuel cells fuelled directly vith non-toxic liquid chemicals (ethanol, in particular, but also other chemicals such as ethylene glycol are possible). Together vith improvement in other fuel cell components (membranes, in particular), ethanol direct fuel cells require the development of ne v more active and stable electrocatalysts. 

In the L79 design, both the gas flow fields and electrodes are made from single sided copper clad circuit board. Copper clad circuit board comes in a variety of sizes and is either clad with copper on one side only, or both sides. Boards also differ in the type of base material they are made of. This fuel cell requires the FR-4 glass epoxy resin base, clad with copper on one side only. We used a 1 ounce, which is coated with copper to a thickness of. 0014". 

Hydrogen was the only really useful non-exotic fuel, but using it with relatively inexpensive nickel catalysts in an alkaline fuel cell required high temperatures and pressures, costly pressure vessels, and ancillary equipment. 

Alkaline fuel cells required very pure hydrogen. That was problematic when hydrogen was produced from common fuels such as natural gas or coal. Any residual C02 in the hydrogen reacts with the liquid alkaline electrolyte, gumming up the electrodes microscopic pores and slowing the overall chemical reactions. 

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