The quantum origin of oxygen storage

In cerium oxide has been elucidated. Many environmentally friendly technologies, such as catalytic converters and solid-oxide fuel cells, exploit an amazing property of solid CeO₂, also known as ceria. Under oxygen-poor conditions, ceria can release oxygen, transforming itself into Ce₂O₃. The Ce₂O₃, in turn, easily takes up oxygen under oxygen-rich conditions and changes back to ceria. Now, physicists from several universities in Sweden offer a detailed quantum-mechanical description of how these reactions occur. The researchers showed that the pivotal transition from CeO₂ to Ce₂O₃ results from the formation of an oxygen vacancy, in which the oxygen leaves behind two electrons that become localized on two nearby cerium ions. The charge on that pair of ions then changes from +4 to +3, and a series of reduced compounds form, ending with Ce₂O₃. The ability of solid cerium oxide to store, transport, and release oxygen is therefore an industrially important example of the quantum process of electron localization. (N. V. Skorodumova et al., Phys. Rev. Lett. 89 , 166601, 2002 http://dx.doi.org/10.1103/PhysRevLett.89.166601 .)