Electronic agglomeration effect of Co-O sites in ultrafine cobalt oxide coupled CNT accelerating ORR kinetic activity for hybrid sodium-air battery

Hybrid sodium-air batteries (HSABs) offer a possible solution for large-scale energy storage due to high theoretical energy density and abundant sodium resource. However, ORR suffers from sluggish kinetics with multielectron transfer step, resulting in high overpotential. Herein, we demonstrated electronic agglomeration effect on CoO/CNT to controllably activate catalytic active species to boost ORR by atomic surface engineering. By virtues of superior electron transfer ability and optimal adsorption energy of reactive species, activities of F- surface-decorated electrode could be greatly improved. DFT revealed that F- induced electronic agglomeration on Co -O sites, resulting in high electron density of Co and intense combination with OH* in the first step. Surprisingly, the F-CoO/CNT showed favorable ORR activity and enabled advanced HSAB with low overpotential gap of 0.14 V. This work provides a new view about atomic and electronic structure engineering for activating active species, which will pave a new way for designing electrode materials.