Fuel cells face acid test

A researcher at the California Institute of Technology has developed an alternative type of fuel cell based on so-called ‘solid acids’.

Scientists have long been studying fuel cells as a long-term alternative to fossil fuels but they are said to have limitations. CALTECH’s Sossina M Haile believes that ‘solid acids’ could resolve some of the problems currently hindering fuel cell research.

Fuel cells convert chemical energy directly into electrical energy. The most common type under development for use in portable power is a polymer electrolyte fuel cell, which must be humidified in order for the fuel cell to function. This type of fuel cell can only operate over a limited temperature range, is permeable, needs many auxiliary components and is said to be less efficient than other types of fuel cells.

Haile, an assistant professor of materials science has developed an alternative type of fuel cell that is not a hydrated polymer, but is based on solid acids such as potassium hydrogen sulphate.

Solid acids can conduct electricity at similar values to polymers, don’t need to be hydrated, and can function at temperatures up to 250 degrees Centigrade. Solid acids are also typically inexpensive compounds that are easy to manufacture.

But until now such solid acids have not been examined as fuel-cell electrolytes because they dissolve in water and can lose their shape at slightly elevated temperatures.

To solve these problems, Haile and her colleagues operated the fuel cell at a temperature above the boiling point of water, and used a solid acid, CsHSO4, that is not very prone to shape changes.

The next challenge, said Haile, is to reduce the electrolyte thickness, improve the catalyst performance, and prevent the reactions that can occur upon prolonged exposure to hydrogen.

‘The system simplifications that come about (in comparison to polymer electrolyte fuel cells) by operating under essentially dry and mildly heated conditions are tremendous,’ said Haile. ‘While there is a great deal of development work that needs to be done before solid acid based fuel cells can be commercially viable, the potential payoff is enormous.’

The US Department of Energy, as part of its promotion of energy-efficient science research, recently awarded Haile an estimated $400,000 to continue her research in fuel cells.

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