At its essence, a fuel cell combines hydrogen and oxygen to form electricity, heat, and water. The source of this hydrogen may be from natural gas, coal, gasoline, diesel, alcohols, or natural decomposition products. Pure hydrogen is the ideal fuel, but it needs to be obtained by processing fossil fuels (natural gas, gasoline, diesel, oil, coal, etc.), biofuels (e.g., landfill gas, anaerobic digester gas, etc.), or chemical intermediates, or must be produced via renewable energy sources through electrolysis of water. Currently pure hydrogen is produced cryogenically at both a great energy and fiscal expense. In this paper, we cover all important fuel reforming processes for generating hydrogen for fuel cells and then discuss the associated reformers. The common techniques utilized for external fuel reforming processes are steam reforming, partial oxidation and autothermal reforming. For high temperature fuel cells, direct and indirect internal reforming techniques are used and will be discussed. The methods for reforming of chemical intermediates (alcohol and ammonia), reforming of bio-fuels and aviation fuels are also discussed in this paper. For low temperature fuel cells such as PEM, carbon monoxide is a poison that adversely affects fuel cell performance. The CO content must be reduced to below 100 ppm. This is accomplished by use of the water-gas shift reaction, preferential oxidation, methanation, or may be accomplished by membrane separation techniques. Special emphasis in this paper will be the challenges and opportunities in fuel processing for fuel cells.

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