In-situ nitrogen-doped carbon nanotube-encapsulated Co9S8 nanoparticles as self-supporting bifunctional air electrodes for zinc-air batteries

A flexible air electrode with excellent activity and stability is essential for flexible zinc-air batteries. In this study, we report the rational design of nitrogen-doped carbon nanotube-encapsulated Co₉S₈ nanoparticles on carbon cloth (Co₉S₈/NCNTs/CC), serving as self-supporting air electrodes for both liquid-state and flexible zinc-air batteries. The Co₉S₈/NCNTs/CC-1 exhibited a half-wave potential of 0.86 V for oxygen reduction reaction (ORR) and achieved a current density of 10 mA cm⁻² for oxygen evolution reaction (OER) at a voltage of only 1.52 V. The well-constructed nanotube on carbon cloth facilitates mass diffusion and electron transfer, while enhancing the mechanical flexibility of the material. Density functional theory (DFT) calculations suggested that the synergistic interaction between Co₉S₈ and NCNTs effectively enhanced the bifunctional electrocatalytic performance of the material. Liquid-state and flexible zinc-air batteries assembled with Co₉S₈/NCNTs/CC-1 demonstrated outstanding charge-discharge capabilities and long-term stability.