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Instant insight: Fuel cells get cooler
27 June 2008
Brett, Atkinson, Brandon and Skinner of the Imperial College Fuel Cell Network, London, UK, look at how advances in materials and engineering are presenting new opportunities for solid oxide fuel cells.
Intermediate temperature solid oxide fuel cells hold the middle ground in the temperature scale of fuel cell operation
Fuel cells are electrochemical energy conversion devices that convert the chemical energy in fuel directly into electricity and heat without combustion. Simplistically, a fuel cell can be viewed as a cross between a battery, which converts chemical energy directly into electrical energy, and a heat engine, a continuously fuelled, air breathing device. There is a range of different fuel cell technologies, each with its own materials set and operation temperature, ranging from room temperature to over 1000 degrees Celsius. However, they all share the characteristics of high efficiency, no moving parts, quiet operation and low or zero emissions.
Advances in the chemistry and processing of materials are allowing the operating temperature of SOFCs to be lowered into the so-called 'intermediate temperature' (IT) region of 500 to 750 degrees Celsius. The IT-SOFC opens up a new range of applications and opportunities for SOFCs in areas formally dominated by PEFCs, while maintaining the ability to operate on hydrocarbon fuels and produce high quality heat.
Operation in the IT range expands the choice of materials and stack designs that can be used compared to conventional high temperature (HT) SOFCs. Lower temperature operation affords more rapid start-up, improved durability, reduced system cost and more robust construction through the use of compressive seals and metallic construction materials (as opposed to the all-ceramic HT-SOFCs).
There are two main routes by which SOFCs can be used at lower temperatures while still attaining comparable performance to the higher temperature technology. The first involves reducing the thickness of the electrolyte to the order of a few 10s of micrometres, so ions can travel more easily through the fuel cell. Alternatively, the same result can be achieved by improving the electrolyte's ionic conductivity at lower temperatures and the electrodes' electrochemical performance.
As with all fuel cells, the cost of IT-SOFCs must be reduced for them to compete in the market with current technologies. Using less, and cheaper, material is necessary; moving to lower temperature operation represents a significant step in this direction. Scientists still need to develop IT-SOFCs with commercially meaningful levels of durability. Fundamental studies are improving our understanding of processes such as electrode sintering, anode-fuel interaction, electrocatalyst poisoning and the mechanical properties of electrolytes and support structures.
Read more in 'Intermediate temperature solid oxide fuel cells' in issue 8 of Chemical Society Reviews.
Link to journal article
Imperial College London Fuel Cell Network
Information on the fuel cell researchers and projects at Imperial College London
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Also of interest
Materials scientists from Spain and the UK have made a cathode material that allows solid oxide fuel cells (SOFCs) to be used at lower temperatures.
A simple iron complex could pave the way for new oxygen reduction catalysts with potential uses in low-temperature fuel cells