Electrochemical engines, fuel cells

Principles of electrochemical engineering, fuel cell reactors, and electrocatalytic reactor design... 

Use of Isotopic Effects in the Determination of Electro-Organic Reaction Mechanisms. Much work has been carried out on the mechanism by which hydrocarbons can be clectrochemically oxidized. Were that easy, it might be possible to use available oil in electrochemical devices (fuel cells) to convert chemical to electrical energy 2—3 times more efficiently than do heat engines (Chapter 13). 

Hydrogen is widely regarded as the ideal or nearly ideal fuel to solve those problems. By definition, it doesn t pollute. Burned or oxidized with atmospheric oxygen, it produces water. (It also produces some nitrogen oxides if combustion occurs with a flame, as in an internal-combustion engine, but no nitrogen oxides are produced in an electrochemically reactive fuel cell.)... 

Various t)q5es of modern power plants can operate on natural gas highly diluted with nitrogen, up to methane content below 50% in electrochemical generators (fuel cells), 40% in spark ignition engines, 30% in conventional gas turbines, 5% in diesel engines, and 1% in gas turbines with catalytic combustion [300]. 

Michael Krumpelt, Ph.D., Manager, Fuel Cell Technology, Argonne National Laboratory Member, American Institute of Chemical Engineers, American Chemical Society, Electrochemical Society (Section 27, Energy Resources, Conversion, and Utilization)... 

Fuel cells, which rely on electrochemical generation of electric power, could be used for nonpolluting sources of power for motor vehicles. Since fuel cells are not heat engines, they offer the potential for extremely low emissions with a higher thermal effidency than internal combustion engines. Their lack of adoption by mobile systems has been due to their cost, large size, weight, lack of operational flexibility, and poor transient response. It has been stated that these problems could keep fuel cells from the mass-produced automobile market until after the year 2010 (5). 

Gottesfeld, S., and Zawodzinski, T. A. (1998). Polymer Electrolyte Fuel Cells, Advances m Electrochemical Science and Engineering, ed. R. Alkire et al. NewYork Wiley. 

Imagine if we could extract significantly more useful energy out of our precious fuel resources Think how remarkable it would be to carry out combustion processes at efficiencies not possible in even the most sophisticated heat engines. These are not empty dreams. Such a device was first demonstrated in 1839. Called a fuel cell, this electrochemical device may eventually reshape major energy use patterns throughout society. 

In practice the situation is less favorable due to losses associated with overpotentials in the cell and the resistance of the membrane. Overpotential is an electrochemical term that, basically, can be seen as the usual potential energy barriers for the various steps of the reactions. Therefore, the practical efficiency of a fuel cell is around 40-60 %. For comparison, the Carnot efficiency of a modern turbine used to generate electricity is of order of 50 %. It is important to realize, though, that the efficiency of Carnot engines is in practice limited by thermodynamics, while that of fuel cells is largely set by material properties, which may be improved. 

Gottesfeld, S., and T. A. Zawodzinski, Direct methanol oxidation fuel cells from a 20th century electrochemist s dream to a 21st century emerging technology, in Electrochemical Science and Engineering, R. C. AUdre et al., Eds., Vol. 5, WUey, New York, 1988. 

Scientific American published a special issue on fuel cells in July 1999. Alternatively, A. John Appleby s introductory article The electrochemical engine for vehicles is a good read the Internet sites http //www.chemcases.com/cells/index.htm, http //www.fuelcells.org and http //www.howstujfworks.com/fuel-cell.htm and fuel-cell2.htm are also worth a try. 

Fuel cell vehicles are viewed as one of the best long term options. A hydrogen fuel cell vehicle has advantages over alternatives, such as hybrid vehicles which combine IC engines with electrochemical batteries and still require petrochemical fuels that exhaust carbon dioxide and pollutants. 

S. Gottesfeld, T.A. Zawodzinski, "Polymer Electrolyte Fuel Cells," Advances in Electrochemical Science and Engineering, Volume 5, edited by R.C. Alkire, et al., Wiley-VCH, 1998. 

His research interests are generally in high-temperature and solid-state chemistry of materials, including electrochemical devices (e.g., chemical sensors and fuel cells) and the chemical stability of materials (e.g., high-temperature oxidation). Dr. Fergus is an active member of the Electrochemical Society, the Metals, Minerals and Materials Society, the American Ceramics Society, the Materials Research Society, and the American Society for Engineering Education. 

Dynamic characteristics of a fuel cell engine are of paramount importance for automotive application. Three primary processes govern the time response of a PEFC. They are (1) electrochemical double-layer discharging, (2) gas transport through channel and GDL, and (3) membrane hydration or dehydration (i.e., between a dry and a hydrated state). The time constant of double-layer discharging is between micro- and milliseconds, sufficiently short to be safely ignored for automotive fuel cells. The time constant for a reactant gas to transport through GDL can be estimated simply by its diffusion time, i.e.,... 

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