Defect Chemistry and Catalytic Activity of Nanosized Co3O4

Nanometric cobalt oxide Co3O4 powders made of 4 nm isotropic particles, directly precipitated from Co2+ aqueous solutions under alkaline and oxidizing conditions, are found to exhibit abnormal X-ray diffraction intensities, mainly in (111) and (220) reflections, because of a significant amount of displaced Co atoms from ideal 8a and 16d positions to interstitial 48f and 16c sites. Upon heating, the Co/O stoichiometry is maintained and the delocalized atoms progressively migrate to stable positions through empty neighboring sites. Despite the presence of such defects, the order of reaction (n ≈ 1) and the activation energy (Ea ≈ 60 ± 5 kJ/mol) versus the decomposition of diluted solutions of hydrogen peroxide solutions is found to be similar to bulk nonfaulted Co3O4 materials, but the intrinsic rate constants k20 °C are found to be proportionally enhanced by both the defect and microstrains levels. Last, a careful selection of monolithic samples, so as to keep away the catalytic influence of the intercrystallites reactive grain-boundaries, has enabled us to precisely study and isolate the role of the structural characteristics on the catalytic activity of Co3O4 toward H2O2 decomposition. The catalytic activity of such divided oxides toward this reaction is also put forward as a fast selection tool for catalysts in Li-oxygen secondary cells.