Fuel cell compression

Mercury and water porosimetry measurements have shown that the GDL pore structure changes during lifetime tests. Large pore (30-60 um diameter) volume has decreased, while small-pore volume increases. The loss in large-pore volume is likely due to irreversible fuel cell compression [118]. 

On the same topic of DMFC performance with supported vs. unsupported catalysts Smotkin and co-workers concluded that at 363 Kthe supported PtRu (1 1) catalyst with a toad of 0.46 mg cm performed as welt as an unsupported PtRu (1 1) with over four times higher load, i.e., 2 mg cm [266]. It is likely that these differences between various studies are related not only to the intrinsic activity of the respective anode catalys layers but also to the manufacturing procedures such as catalyst layer preparation and application techniques, MEA hot pressing conditions (temperature, pressure and time), presence or absence of other binders (such as PTFE) and fuel cell compression. All these MEA manufacturing variables can affect, in a poorly understood manner at present, the structure, morphology and composition of the catalyst layer in the operating fuel cell. Therefore, in fuel cell experiments it is difficult to isolate the truly physico-chemical effect of the support on the catalytic activity. 

Watt Fuel Cell, Compressed Hydrogen Cylinder... 

Strobel R, Oszcipok M, Fasil M, Rohland B, Jorissen L, Garche J. 2002. The compression of hydrogen in an electrochemical cell based on a PE fuel cell design. J Power Sources 105 208-215. 

A fuel cell system for automobile application is shown in Figure 1.5 [41]. At the rated power, the PEMFC stack operates at 2.5 atm. and 80°C to yield an overall system efficiency of 50% (based on lower heating value of hydrogen). Compressed hydrogen and air are humidified to 90% relative humidity at the stack temperature using process water and heat from the stack coolant. A lower system pressure is at part load and is determined by the operating map of the compressor-expander module. Process water is recovered from spent air in an inertial separator just downstream of the stack in a condenser and a demister at the turbine exhaust. 

It is to be noted that the difference in dissipation of energy between the thermal energy demanded by organic chemical hydrides and the mechanical energy by compression or liquefaction of hydrogen is quite significant because the former is supplied as waste heat, whereas the latter is lost at the site of hydrogen utilization for fuel cells or ICEs. 

S. Reckers et al., Leakage investigations of compressive metallic seals in SOFC stack, in Proceedings of the Fifth European Solid Oxide Fuel Cell Forum, J. Huijsmans (ed.), 1-5 July 2002, Lucerne, Switzerland, 2002, pp. 847-854. 

Y.-S. Chou and J.W. Stevenson, Phlogopite Mica-Based Compressive Seals for Solid Oxide Fuel Cells Effect of Mica Thickness, Journal of Power Sources, 124, pp. 473 178 (2003). 

Hydrogen gas is odorless and colorless. It burns almost invisibly and a fire may not be readily detected. Compressed hydrogen gas could be ignited with the static discharge of a cell phone. But, an accident may not cause an explosion, since carbon fiber reinforced hydrogen tanks are nearly indestructible. There is always the danger of leaks in fuel cells, refineries, pipelines and fueling stations. 

Compressed gas is being used in most current demonstration vehicles. But, the path to commercialization of any major new technology is a long one. In 2003 Toyota recalled some of its hydrogen-powered fuel cell vehicles when a leak was found in the fuel tank of one of the cars leased to Japan s Ministry of the Environment. The leak was found when a driver at the ministry heard a strange noise in the car when he was filling up the hydrogen tank. The problem was quickly identified and fixed a few weeks later. 

An onboard hydrogen tank has several problems since hydrogen leaks easily, is hard to store and hard to compress and burns quickly. Overcoming all these concerns has been expensive but most of the major auto companies has solved these problems for the most part in their prototype fuel cell vehicles. Refueling tends to be difficult although there are now a number of hydrogen refueling stations in use around the world. 

Power systems that run on compressed gases such as propane, methane, or hydrogen are problematical. Range may be limited since distribution systems are not in place and each station pump could cost 30,000. So-called synthetic fuels could be used directly in engines or to generate electricity from fuel cells for electric motors. Other combustion engines such as the sterling motor may also become options. 

In 2004 a retail hydrogen fueling station opened in Washington D.C. in a partnership between Shell and GM to develop hydrogen-fueled vehicles on a commercial scale. The station will service GM fuel cell vehicles. Both compressed and liquid hydrogen refueling are available. 

Individual drive motors on each of the vehicle s four wheels allows a fuel cell powered all wheel drive system. Three tanks hold Hy-wire s hydrogen fuel, compressed at 5,000 pounds per square inch. These were developed by Quantum Fuel Systems, the company that developed the industry s first 10,000-psi tanks, which could allow a fuel cell car to have a driving range of 230 miles. 

Ford planned to produce a fuel cell family car based on the aluminum and composite P2000 which is like the Ford Contour but weighs a thousand pounds less. In 1997, Ford announced that its fuel cell car would carry compressed hydrogen, but the fuel storage question may be still open. 

Hyundai introduced its new i-Blue Fuel Cell Electric Vehicle. The i-Blue platform incorporates Hyundai s third-generation fuel cell technology and is powered by a 100-kW electrical engine and fuel cell stack. It is fueled with compressed hydrogen at 700 bar stored in a 115 liter tank. The i-Blue is capable of running more than 600-km per refueling stop and has a maximum speed of 165-km/h. 

Some computer models of fuel cell cars show the power needed at the wheel which is computed from the weight of the car, energy of the fuel, accessories and other variables including mileage. An onboard reformer has been shown to provide 70 miles per gallon, but compressed hydrogen... 

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