Bifunctional Composite Catalysts Using Co sub(3)O sub(4) Nanofibers Immobilized on Nonoxidized Graphene Nanoflakes for High-Capacity and Long-Cycle Li-O sub(2) Batteries

Designing a highly efficient catalyst is essential to improve the electrochemical performance of Li-O sub(2) batteries for long-term cycling. Furthermore, these batteries often show significant capacity fading due to the irreversible reaction characteristics of the Li sub(2)O sub(2) product. To overcome these limitations, we propose a bifunctional composite catalyst composed of electrospun one-dimensional (1D) Co sub(3)O sub(4) nanofibers (NFs) immobilized on both sides of the 2D nonoxidized graphene nanoflakes (GNFs) for an oxygen electrode in Li-O sub(2) batteries. Highly conductive GNFs with noncovalent functionalization can facilitate a homogeneous dispersion in solution, thereby enabling simple and uniform attachment of 1D Co sub(3)O sub(4) 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 Co sub(3)O sub(4) NFs with large surface area, (ii) facile electron transport via interconnected GNFs functionalized by Co sub(3)O sub(4) NFs, and (iii) fast O sub(2) diffusion through the ultrathin GNF layer and porous Co sub(3)O sub(4) NF networks.