Graphene oxide induced assembly and crumpling of Co₃O₄ nanoplates

Cobalt (II, III) oxide (Co₃O₄) has been widely studied and applied in various fields, however, it suffers from slow mass and electron transfer during applications. Herein, crumpled Co₃O₄ and Co₃O₄/reduced graphene oxide (rGO) with tunable 2D-in-3D structures were prepared by combining spray pyrolysis with a graphene oxide (GO) template. The 2D Co₃O₄ nanoplates were interconnected with each other to form a 3D ball with many wrinkles, resulting in defect enrichment on the abundant boundaries of the nanosheets, which provided more active sites for catalytic reactions. In addition, the unique 2D-in-3D structure allowed fast mass transfer and structural stability. Furthermore, the assembled structure could be understood as being composed of uniformly distributed oxygen-containing functional groups pinning metal cations on the GO surface through electrostatic interaction, and the 2D structure of the GO enabled the in situ converted Co₃O₄ to grow along the GO surface with excellent dispersion. Taking advantage of the above, the Co₃O₄/rGO balls demonstrated an excellent oxygen evolution reaction performance, an overpotential of 298 mV at a current density of 10.0 mA cm^-2 and a current density of 115.9 mA cm^-2 at the overpotential of η = 500 mV.