In situ grown Co₃O₄ nanocubes on N-doped graphene as a synergistic hybrid for applications in nickel metal hydride batteries

The development of high-power batteries for applications in electric vehicles, power tools, military devices, etc. has attracted great attentions in recent years. Here the synergistic effect between Co₃O₄ nanocubes and N-doped graphene has been considered to focus on the major obstacle of the sluggish kinetics of carrier transport and electrochemical reaction during charging/discharging. As an example, we have fabricated the Co₃O₄ nanocubes/N-doped graphene hybrid material and combined it with hydrogen storage alloys. The as-fabricated composite exhibits superior rate performance for applications in nickel metal hydride battery. An ultra-high capacity of 223.1 mAh g⁻¹ is achieved at a specific current of 3000 mA g⁻¹, which is 3.2 times that of the commercial alloy electrode (68.7 mAh g⁻¹). Such remarkable high-rate dischargeability originates from the unique three-dimensional integrated porous structure of Co₃O₄/N-doped graphene, which provides: (1) small internal resistances due to the conductive substrate of N-doped graphene; (2) high electrocatalytic activity of Co₃O₄ nanocubes; (3) a suppression of re-stacking of N-doped graphene nanosheets; and (4) efficient ion and electron pathways and also short transport distances.