Tuning the Electronic Bandgap: An Efficient Way To Improve the Electrocatalytic Activity of Carbon-Supported Co3O4 Nanocrystals for Oxygen Reduction Reactions

The achievement of crystal-lattice tuning along low Miller index planes to decrease the bandgap of spinel transition-metal oxides may be an effective way to enhance their electrocatalytic activity for the oxygen reduction reaction (ORR). Herein, we have prepared spherical Co3O4 nanoparticles with a preferred orientation along the (111) plane by direct nucleation and growth of the oxide on graphitized carbon black (GCB). The formation of the preferred (111) oxide is attributed to a unique chemical interaction at the interface between Co3O4 and carbon, which results in covalent C-O-Co bonds in the hybrid. Electrocatalysis experi-ments in an alkaline environment revealed that the electrocatalytic activity for ORR on the preferred (111) oxide increased as a function of the degree of crystal-lattice orientation, which implies a closely intrinsic correlation between the predominant (111) plane and the catalytic activity. Because Co2+ cations are enriched in this plane, they possess a narrow bandgap and unfilled conduction bands at low energy with respect to Co3+ ions in the preferred (111) Co3O4, which can contribute to the absorption and activation of active oxygen and lead to improved ORR activity.