3D Carbon Framework-supported CoNi Nanoparticles As Bifunctional Oxygen Electrocatalyst For Rechargeable Zn-air Batteries

The growing demand for energy resulting in rapid consumption of fossil fuels,outbreak intensified environmental issues.In order to improve this situation,the utilization of renewable resources is essential.One of the key factors restricting the development of renewable resources is the cost pressure.Rechargeable Zn-air batteries have attracted extensive attention due to their remarkable high theoretical energy output(1086 Wh kg_Zn^-1),resource abundance,low cost,high safety performance and eco-friendliness.It has broad application prospects in electric vehicles,portable power and large storage convenience.Electrocatalysts for oxygen-reduction and oxygen-evolution reactions（ORR and OER,respectively）are crucial for Zn-air batteries.For the large-scale implementation of rechargeable Zn-air batteries,it is highly desirable to design an optimal dual-function oxygen electrocatalyst with low cost and high activity.On the other hand,it is necessary to rationally design the electrode structure of air electrodes to maximize the catalytic effect of catalysts and improve the performance of batteries.Herein,a novel bifunctional electrocatalyst with CoNi alloy nanoparticles supported by a butterfly wing-derived carbon framework（denoted as CoNi/BCF）was synthesized via a pyrolysis method.The obtained CoNi/BCF exhibited excellent oxygen electrocatalytic activity and stability in terms of a positive halfwave potential（0.80 V）for the oxygen reduction reaction（ORR）and a low overpotential(370 mV at 10 mA cm^-2)for the oxygen evolution reaction（OER）.Remarkably,the high bifunctional ORR/OER activity(ΔE_{（ORR–OER）}=0.80 V)also endows an excellent Zn-air battery performance with a high energy density of 853.1 mWh g_Zn^-1,a peak power density of 155.1 mW cm^-2,and an excellent cyclability of over 180 cycles at 10mA cm^-2.The satisfactory electrocatalytic performance is due to the synergetic effect between CoNi alloy nanoparticles and nitrogen-doped carbon framework,which includes the high conductivity,highly dispersed active sites and optimized electronic configuration and reaction pathways.Additionally,the smart structures of butterfly wings endow the hybrid catalyst with a large surface area,which is beneficial for the mass transfer,active sites exposure and the fixation of alloy nanoparticles.Our work presents a strategy to take full advantage of natural organisms,rich elements,and naturally optimized smart structures combined in a two-in-one solution,leading to significant improvements in the electrochemical performance.The realization of rechargeable Zn-air batteries also paves a new way for the design and development of efficient and stable electrocatalysts for energy conversion and storage devices.