Stable enzyme-modified graphite electrodes could be used in fuel cells, according to researchers in the UK.

Laccases are copper-containing enzymes that use electrons to reduce oxygen to water efficiently, making them of interest as electrocatalysts at the cathodes of hydrogen-oxygen fuel cells. In this type of fuel cell, hydrogen is oxidised to hydrogen ions and electrons, which flow to the cathode (supplying power) where they reduce oxygen.

Fraser Armstrong and colleagues at the University of Oxford have chemically attached anthracene to graphite electrodes to form a stable attachment between the electrode and laccase. Armstrong described anthracene as 'a long hydrophobic molecule, similar to laccase's own substrate molecules, which can penetrate the active site pocket and approach closely to one of the copper atoms' where the oxygen reduction takes place. The anthracene not only binds the laccase to the electrode, but, as it can conduct electrons, it also delivers them deep into the enzyme close to the site for oxygen reduction.

The anthracene 'plug' modification of the electrode is essential to provide the high and long-term oxygen-reduction activity. Without it, the electrons are not delivered efficiently into the enzyme and the binding of the laccase to the electrode is not stable, both of which leads to reduced activity. The ability to use graphite is also an advantage; it is relatively cheap compared to precious metals, such as gold, which have been previously used as electrodes for laccases.

To complete the fuel cell, Armstrong said that in future research they would like to 'identify rational attachment strategies for other enzymes, particularly hydrogenases, which can be incorporated with laccases to produce small fuel cells'.

Nicola Convine