Carbon nanotubes for fuel cells

The several approaches being pursued for fuel cells vary in their chemical reactions, materials, and optimal operating conditions, but they share a basic configuration (see Physics Today, November 1994, page 54, and October 2006, page 38). A fuel, often hydrogen, is oxidized at the anode, where it liberates electrons. The electrons travel through and power an external circuit and eventually reach the cathode, where oxygen is reduced. Meanwhile, to complete the redox reaction, ions travel through an electrolyte that separates the electrodes. In alkaline fuel cells, first developed for the Apollo space missions in the 1960s, oxygen combines with water and electrons at the cathode to form hydroxyl ions (OH⁻) that travel through an aqueous alkaline electrolyte to produce water by combining with protons from the anode. Commercialization of those fuel cells, however, has been limited by the high cost of the platinum used for...