SOFC vs PEM

Solid oxide fuel cells required some technical innovations to make a practical unit available to the market. Global's innovations have produced a very simple design that allows common materials to be used in construction of the fuel cell units. A strategic partnership with European companies involved in the development of the SOFC gave Global the final pieces of the puzzle. 

When the SOFC is compared to its closest rival the Proton Exchange Membrane fuel cell, the SOFC outperforms the PEM in most categories. The SOFC operating temperature is a major advantage over its competitors. Operation at 650C to 700C allows for cheaper materials to be used, which cuts down on production costs. The reforming process can be incorporated internally into the fuel stack housing, eliminating the need for an expensive and inefficient external reforming process. The heat also increases overall efficiency of the unit taking the SOFC from its basic efficiency of 60% into the 80%+ range. This high operating temperature also makes the SOFC tolerant to impurities that foul the lower operating temperature fuel cells. 

The SOFC design can easily be adapted to any hydrocarbon gas. Recently Global and Delphi Automotive announced a successful test of a gasoline fueled SOFC. This will allow the Global unit to use the existing fuel infrastructure, PEMs require methanol and hydrogen to operate effectively, presently both fuels require a massive outlay of capital to get to retail pumps.  

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Proton Exchange Membrane Fuel Cells

The PEM has been successfully developed to the point that demonstrative vehicles have been produced. There a several problems that are currently holding the PEM from becoming a commercially viable product. The cost of production has been a major problem that PEM manufacturers are wrestling with. Expensive materials and reformers of hydrocarbon gas are the major costs of production. 

Also water management inside the units inflate the production costs. The water pumps and sensors also take away from efficiency of the unit. The gas reformers have to take the hydrocarbon gas from storage temperature, heat to 700C, reform the gas and then cool the gas for introduction into the fuel cell stack. The reforming process is the major reducer of overall performance, taking the PEM from a basic 50% efficiency to the 40% efficiency range. Innovations in reformers are taking place, but to date a practical, reliable and cost effective hydrocarbon reformer for PEMs has yet to be developed.     

Fuel Cell Comparison Article

Fueling the Cells

While hydrogen is the fuel for all fuel cells, a practical and safe storage system for transportation use has yet to be produced. In the meantime the best thing environmentally is to reform hydrocarbon gas for fuel cell use. Reforming hydrogen from hydrocarbon gas or from water produces carbon dioxide and or carbon monoxide. Polluting NOx emissions that internal combustion engines produce, are eliminated with fuel cell operation.

The PEM would require methanol or hydrogen to operate in automotive applications. Methanol is produced primarily from coal or natural gas. Methanol is comparable to gasoline and there's some debate over safety issues and environmental concerns that methanol poses. The Alternative Fuel Risk Assessment presented the U.S. government suggests that those concerns are well founded.

Comparison Chart