This project is developing multi-walled carbon nanotubes riddled with defects and impurities on the outside to replace platinum and palladium catalysts used in lithium-air batteries. Such batteries are promising due to their ultra-high theoretical energy density, which is more than 10 times higher than today's best lithium-ion technology. However, platinum and palladium are very expensive and thus impractical for large-scale commercialization. In addition, lithium-air cells to date have been relatively inefficient with short life cycles. A major research goal for several decades has been to develop a low-cost, high-performance alternative catalyst. Among the most promising is the carbon nanotube – a rolled-up sheet of pure carbon, called graphene, that's one atom thick and more than 10,000 times narrower a human hair. Carbon nanotubes and graphene are excellent conductors of electricity and relatively inexpensive to produce.
This project showed that shredding the outer wall using chemicals enhanced the catalytic activity in nanotubes, while leaving the inner walls intact maintained the tubes’ ability to conduct electricity. The resulting iron and nitrogen impurities promote the formation of catalytic sites. A single-wall carbon nanotube could not enhance its catalytic activity without degrading its electrical property. Using their novel hybrid material, the researchers have designed and fabricated lithium-air coin cells. Researchers found that the catalytic activity of the nanotubes is very close to platinum in speeding up the chemical reactions that convert hydrogen and oxygen to water, and release electricity. The cell also shows better charge-discharge cycling stability than that with platinum catalyst. However, the cell does not charge as well as batteries using other catalysts, including platinum. Further effort is needed to understand and improve electrocatalysis in the charging reactions, in order to achieve efficient and reliable lithum-air batteries with high energy density.