Bifunctional Composite Catalysts Using Co₃O₄ Nanofibers Immobilized on Nonoxidized Graphene Nanoflakes for High-Capacity and Long-Cycle Li-O₂ Batteries

Designing a highly efficient catalyst is essential to improve the electrochemical performance of Li-O₂ batteries for long-term cycling. Furthermore, these batteries often show significant capacity fading due to the irreversible reaction characteristics of the Li₂O₂ product. To overcome these limitations, we propose a bifunctional composite catalyst composed of electrospun one-dimensional (1D) Co₃O₄ nanofibers (NFs) immobilized on both sides of the 2D nonoxidized graphene nanoflakes (GNFs) for an oxygen electrode in Li-O₂ batteries. Highly conductive GNFs with noncovalent functionalization can facilitate a homogeneous dispersion in solution, thereby enabling simple and uniform attachment of 1D Co₃O₄ NFs on GNFs without restacking. High first discharge capacity of 10 500 mAh/g and superior cyclability for 80 cycles with a limited capacity of 1000 mAh/g were achieved by (i) improved catalytic activity of 1D Co₃O₄ NFs with large surface area, (ii) facile electron transport via interconnected GNFs functionalized by Co₃O₄ NFs, and (iii) fast O₂ diffusion through the ultrathin GNF layer and porous Co₃O₄ NF networks.