A simple iron complex could pave the way for new oxygen reduction catalysts with potential uses in low-temperature fuel cells, say US scientists.

The complex made by Roman Boulatov's team, at the University of Illinois at Urbana-Champaign, may offer an alternative to expensive platinum catalysts currently used for reducing molecular oxygen - the energy-releasing conversion of oxygen into water in fuel cells.

Boulatov's catalyst is a heme - an iron complex of a porphyrin ligand -attached to a single imidazole ligand. He explained the significance of the ligand: 'Isolated heme is a poor catalyst for oxygen reduction, but coordination to the right ligand, such as imidazole, can turn it into a good catalyst.'

The team has overcome the usual problems associated with imidazole-linked complexes, which are usually either unstable in solution or complicated and expensive to produce. The complex is made in a few short steps, exists as a stable dimer and has 'reactivity comparable to its more complex and expensive cousins', Boulatov said.

To develop these complexes into oxygen reduction catalysts, knowledge of how the enzyme cytochrome oxidase uses the heme group to reduce oxygen will be exploited, explained Boulatov. The realistic, yet challenging, goal is to use the catalysts in low-temperature fuel cells, he said. 'Porphyrin chemistry offers many opportunities to fine-tune metalloporphyrin catalysts. However, significant advances in our understanding of the catalysts are required before rational design becomes possible.'

Jon Silversides