A future technology enabling 80% or more greenhouse gas emission reduction is that of fuel cells. The difference between a fuel cell and a battery is that batteries have their energy stored inside, whereas fuel cells generate electricity from external fuel that can be refilled. At the moment hydrogen fuel cells are still under development, but their main advantage over current battery driven electric vehicles are their short refueling time. It takes several minutes to replace a hydrogen fuel tank, whereas charging batteries of electric vehicles regularly still takes several hours. Other advantages of fuel cells compared to batteries are their longer life time, their continued efficiency vs batteries whose efficiency decreases over time, and the reduced environmental impact in comparison with batteries that require more recycling processes.
NIMS has two teams working on fuel cell developments. One is the Polymer Electrolyte Fuel Cell Group led by Je-Deok Kim. This group is developing new conducting electrolyte membranes for alternate temperature fuel cells and new catalyst electrode materials. Another group is the Solid Oxide Fuel Cell Materials Design Group led by Toshiyuki Mori. Their goal is to increase fuel cell efficiency, by developing an optimum of materials on the active solid electrolyte/electrode interface and enable high speed ion diffusion pathways.
The main difference in functioning of these two types of fuel cells is explained below:
"Proton Exchange Membrane (PEM) fuel cells work with a polymer electrolyte in the form of a thin, permeable sheet. Efficiency is about 40 to 50 percent, and operating temperature is about 80 degrees C (about 175 degrees F). Cell outputs generally range from 50 to 250 kW. The solid, flexible electrolyte will not leak or crack, and these cells operate at a low enough temperature to make them suitable for homes and cars. But their fuels must be purified, and a platinum catalyst is used on both sides of the membrane, raising costs."
"Solid Oxide fuel cells (SOFC) use a hard, ceramic compound of metal (like calcium or zirconium) oxides (chemically, O2) as electrolyte. Efficiency is about 60 percent, and operating temperatures are about 1,000 degrees C (about 1,800 degrees F). Cells output is up to 100 kW. At such high temperatures a reformer is not required to extract hydrogen from the fuel, and waste heat can be recycled to make additional electricity. However, the high temperature limits applications of SOFC units and they tend to be rather large. While solid electrolytes cannot leak, they can crack."
[Source: http://americanhistory.si.edu/fuelcells/basics.htm]
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