Ordered mesoporous Co3O4 spinels as stable, bifunctional, noble metal-free oxygen electrocatalysts

We report the use of noble metal-free ordered mesoporous Co3O4 spinels (meso-Co3O4), templated from KIT-6 mesoporous silica, as highly active and stable bifunctional electrocatalysts for both oxygen evolution and reduction reactions (OER and ORR, respectively). The meso-Co3O4 nanostructures showed high activity for OER in an alkaline medium (0.1 M KOH), which makes them comparable to the most active Ir/C catalyst and better than Co3O4 nanoparticles (NPs) and the Pt/C catalyst. Furthermore, meso-Co3O4 exhibited enhanced stability, compared to Co3O4 NPs. The enhanced activity and stability of meso-Co3O4 over Co3O4 NPs could be attributed to its high surface area and structural stability of the gyroid network structure in the meso-Co3O4 catalysts. The meso-Co3O4 nanostructures also showed promising activity for ORR and exhibited a methanol-tolerance superior to the Pt/C catalyst. The total overpotential of meso-Co3O4 for OER (at 10 mA cm(-2)) and ORR (at -3 mA cm(-2)) was 1.034 V, which is on a par with noble metal-based catalysts. This work demonstrates that directing metal oxides into mesostructures is a promising means of preparing highly active, stable, bifunctional oxygen electrocatalysts that can potentially replace expensive noble metal-based catalysts. This design strategy can be extended to other reactions relevant to energy conversion and storage applications.