US material scientists have developed a small, propane-powered solid oxide fuel cell that acts as its own heat source.

US material scientists have developed a small, propane-powered solid oxide fuel cell (SOFC) that acts as its own heat source. The breakthrough reflects a growing trend away from hydrogen fuels, which have yet to succeed, towards less radical technologies for energy generation.

The main advantages of SOFCs over other fuel cell technologies are that they incorporate a solid rather than liquid electrolyte and are able to generate electricity directly from hydrocarbon fuels such as natural gas and petrol. In the most advanced versions, a combination of the hydrocarbon fuel and oxygen is introduced into a single chamber, where the anode partly oxides the hydrocarbon fuel to H2 and CO. Using oxygen ions generated by the cathode, the anode then converts these compounds to H20 and CO2, producing electricity in the process.

But a major disadvantage of SOFCs is that they need to be heated to 700-1000?C in order for the anode to catalyse the oxidation reactions. This is holding back the development of small-scale SOFCs. 

Material scientists at several centres in the US led by Sossina Haile at the California Institute of Technology (Caltech), Pasadena, have now found a solution to this problem. They developed a small propane-powered SOFC, around the size of a watch battery, in which the anode is covered with a thin catalytic film of ruthenium metal particles mixed with cerium dioxide.

This catalytic film allows the oxidation reactions to occur at lower temperatures, which means that the heat produced by the reactions is all that is needed to keep the fuel cell working. The new cell will maintain a temperature of 580?C with no external heating over the course of 200 hours. It is an operating temperature sufficient to generate a power output of around 350mW, which means that two of these SOFCs could drive an MP3 player.

There are still problems - for instance, the fuel cell needs to be heated up initially - but Haile and her team are confident they can solve these with design improvements. Jon Evans

References

et alNature435, 795