Encapsulating CoNi nanoparticles into nitrogen-doped carbon nanotube arrays as bifunctional oxygen electrocatalyst for rechargeable zinc-air batteries.

The high theoretical specific energy and environmental friendliness of zinc-air batteries (ZABs) have garnered significant attention. However, the practical application of ZABs requires overcoming the sluggish kinetics associated with oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, 3D self-supported nitrogen-doped carbon nanotubes (N-CNTs) arrays encapsulated by CoNi nanoparticles on carbon fiber cloth (CoNi@N-CNTs/CFC) are synthesized as bifunctional catalysts for OER and ORR. The 3D interconnected N-CNTs arrays not only improve the electrical conductivity, the permeation and gas escape capabilities of the electrode, but also enhance the corrosion resistance of CoNi metals. DFT calculations reveal that the co-existence of Co and Ni synergistically reduces the energy barrier for OOH conversion to OH, thereby optimizing the Gibbs free energy of the catalysts. Additionally, analysis of the change in energy barrier during the rate-determining step suggests that the primary catalytic active center is Ni site for OER. As a result, CoNi@N-CNTs/CFC exhibits superior catalytic activity with an overpotential of 240 mV at 10 mA cm toward OER, and the onset potential of 0.92 V for ORR. Moreover, utilization of CoNi@N-CNTs/CFC in liquid and solid-state ZABs exhibited exceptional stability, manifesting a consistent cycling operation lasting for 100 and 15 h, respectively.