In-situ nitrogen-doped hierarchical porous hollow carbon spheres anchored with iridium nanoparticles as efficient cathode catalysts for reversible lithium-oxygen batteries

One of the biggest challenges on the way to the commercialization of lithium-oxygen (Li-O₂) batteries (LOBs) is the exploration of an air electrode with high electronic conductivity, steadily porous architecture, and high-efficiency bifunctional catalytic activity. In this study, nitrogen-doped and iridium decorated carbon spheres with hollow and hierarchical porous structure were successfully fabricated and used as excellent bifunctional electrocatalysts in alkaline aqueous environment as well as in non-aqueous LOBs. This material structure with large pore volume and high specific surface area provides sufficient room and numerous active sites for the deposition of Li₂O₂ product. Moreover, the in-situ nitrogen doping further enhances the electron conductivity as well as the electrocatalytic activity toward oxygen, yielding a gratifying discharge platform potential of 2.77 V, and a high discharge capacity (6849 mAh g⁻¹). After anchoring with Ir nanoparticles, the resulting composite material presented significantly reduced charge overpotential (0.83 V) and improved reversibility. Meanwhile, owing to the synergistic effect among the porous carbon, nitrogen heteroatom, and Ir nanocrystals, the increased discharge capacity of 8239 mAh g⁻¹ and high discharge plateau of 2.80 V were also achieved. Besides, the excellent stability of the recharged air-cathode architecture was confirmed via ex-situ scanning electron microscopy.