Catalysts improve fuel cells

Researchers at the US Department of Energy’s Brookhaven National Laboratory have published details about catalysts that could improve the performance of fuel cells.

The researchers looked at two nanomaterial catalysts, gold-cerium oxide and gold-titanium oxide, which can act to reduce the amount of carbon monoxide (CO) produced by a fuel cell using the water-gas shift (WGS) reaction.

This reaction combines the CO, produced by the hydrogen-rich materials feeding the fuel cell, with water to create additional hydrogen and CO₂. This improves the efficiency of fuel cells by providing more fuel, as well as removing the ‘poisonous’ CO which degrades the platinum catalyst used to convert hydrogen into electricity. The catalysts have enabled the WGS to convert nearly 100 per cent of the CO into CO₂.

‘These nanomaterials have recently been reported as very efficient catalysts for the WGS reaction,’ said Brookhaven chemist, Jan Hrbek. ‘This was a surprising finding because neither bulk gold nor bulk ceria and titania are active as catalysts.’

The researchers used ‘inverse model catalysts’, placing ceria or titania nanoparticles on a pure gold surface to get a better look at the surface interactions.

‘The oxides have unique properties on the nanoscale and are able to break apart water molecules, which is the most difficult part of the WGS reaction,’ added Hrbek. Once the water is dissociated the reaction can continue to eliminate CO.

Fuel cells combine hydrogen and oxygen without combustion to produce direct electrical power and water. They are attractive as a source of power for transportation applications because of their high energy efficiency, the potential for using a variety of fuel sources, and their zero emissions. CO is created during the production of hydrogen from hydrogen-rich materials and gradually reduces the efficiency of the platinum catalyst until it needs to be replaced.

The team plan to continue their study of the catalysts to further explore the reaction mechanism and optimise the performance. Funding is supplied by the US Department of Energy’s Office of Science.