Faced with the challenge of developing low-cost catalysts for some fuel cells and metal–air batteries, researchers have come up with a basic recipe that ensures high catalytic activity in a family of widely used materials.

Perovskite oxides catalyse the oxygen-reduction reaction, a core process in fuel cells and batteries. Yang Shao-Horn and Hubert Gasteiger at the Massachusetts Institute of Technology in Cambridge and their group studied 15 different perovskite oxide materials, which contain transition-metal ions. They found that the materials' catalytic activity in reducing molecular oxygen is strongly dependent on the level of occupancy of the transition metal's eg electron orbital.

Because of various electron interactions between atoms of the oxide, this occupancy level can vary between 0 and 2. With one electron in this orbital, catalytic activity increased by four orders of magnitude compared with oxides that have 0 or 2 electrons in the orbital. An occupancy of less than 1 led to an interaction with the incoming oxygen that was too strong, whereas occupancy of greater than 1 made it difficult for the catalyst to interact with and adsorb the molecule.

Nature Chem. doi:10.1038/nchem.1069 (2011)