Lithium batteries that utilize oxygen as the cathode material are very promising owing to their extremely high theoretical capacity of almost 12,000 Wh kg-1. In these lithium-air batteries, oxygen is adsorbed directly from the atmosphere when required rather than being stored in the battery itself. In practice, a combination of carbon powder, oxygen, oxygen reduction catalyst and a binder is used in the air cathode. Rechargeability of the battery is dependent on the catalyst, and another important parameter, the specific capacity, is also sensitive to the nature of the catalyst. Hence, identification of suitable catalyst materials is crucial to achieving desirable performance characteristics close to the theoretical limit.
The University of Connecticut’s Steven Suib and coworkers have now reported a promising new oxygen reduction catalyst composed of octahedral molecular sieves of the the gamma form of manganese oxide (gamma-MnO2) and a small amount of titanium. Synthesized via a simple one-step precipitation method, in which the Ti acts as a morphology-directing agent, hollow spheres with a high surface area and enhanced catalytic activity are obtained. The researchers demonstrate that a high-charge storage capacity (2.3 Ah g-1 carbon) can be achieved in Li-air batteries utilizing this material. Although often used in traditional batteries, this is the first time that gamma-MnO2 materials have been applied in this manner to Li-air batteries. The advantageous properties of this material are not restricted to batteries either: Strong conversion rates for the atmospheric oxidation of toluene (a notoriously difficult liquid phase toluene oxidation process) are also reported.