Fabrication of three-dimensional ordered macroporous spinel CoFe2O4 as efficient bifunctional catalysts for the positive electrode of lithium-oxygen batteries.

Three-dimensionally ordered macroporous (3DOM) CoFe2O4 (CFO) catalysts were prepared by using the colloidal crystal templating method to be used as bifunctional catalysts of Li-O2 battery positive electrodes. In order to study the relationship between the macropore diameter and charge/discharge behavior, 3DOM CFO catalysts with two different pore diameters of 140 and 60 nm were prepared. The physicochemical properties of the 3DOM CFO catalysts were investigated by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy. When the 3DOM CFO catalyst with a pore diameter of 140 nm (CFO@140) was used in the O2-electrode of Li-O2 batteries, it exhibited a substantially enhanced discharge capacity (ca. 11 658.5 mA h g-1) in the first cycle. Moreover, the Li-O2 cells with the CFO@140 catalyst showed cycling stability over 47 cycles at a limited capacity of 500 mA h g-1 with a reduced potential polarization of 1.13 V, as compared with that with Ketjen Black carbon and the 3DOM CFO of 60 nm pore diameter (CFO@60). Their high cycling stability, low overpotential, high round-trip efficiency, and high rate performance suggest that these 3DOM CFO catalysts could be promising O2-electrode catalysts for next-generation lithium-oxygen batteries.