Exfoliated Single Layers of Layered Cobalt Hydroxide for Ultrafine Co₃ O₄ Nanoparticles on Graphene Nanosheets as an Efficient Electrocatalyst for Oxygen Reduction

A highly effective way to produce an oxygen reduction electrocatalyst was developed through the self-assembly of exfoliated single layers of cobalt hydroxide (Co(OH)₂ ) and graphene oxide (GO). These 2D materials have complete contact with one another because of their physical flexibility and the electrostatic attraction between negatively charged GO and positively charged Co(OH)₂ layers. The strong coupling induces transformation of the Co(OH)₂ single layer into a discrete nanocrystal of spinel Co₃ O₄ with an average size of 8 nm on reduced GO (RGO) during calcination, which could not be obtained with bulk-layered cobalt hydroxide because of its rapid layer collapse. The ultrafine Co₃ O₄ /RGO hybrid exhibited not only comparable performance in the oxygen reduction reaction but also higher durability compared with the commercial 20 wt % Pt/C catalyst.