Preparation And Electrocatalytic Performance Of Iron-nickel-Nanoparticle-Embedded N-doped Carbon Nanotube Arrays

Rechargeable zinc-air battery is a high energy density,safe and pollution-free energy storage and conversion device,suitable for electric vehicles and various electronic products.It's performance is mainly affected by the slow kinetics of cathodic oxygen reduction reaction(ORR)and oxygen precipitation reaction(OER).Therefore,bifunctional electrocatalysts are usually used to accelerate the kinetic process of cathode reactions.In the rechargeable zinc-air battery system,the precious metal materials Pt and Ir O₂/Ru O₂ are mainly used as ORR and OER catalysts,but there are still many problems hindering the commercial application of the rechargeable zinc-air battery.Firstly,these catalyst materials are expensive precious metals;secondly,their stability performance is average.Therefore,it is necessary to develop a low-cost bifunctional catalyst with high stability for the popularization of rechargeable zinc-air batteries.The transition metals with abundant reserves have moderate adsorption capacity of reactants in catalytic reactions due to the unfilled state of valence d orbitals,so they have the potential catalytic capacity of OER or ORR.Carbon materials have been used in the field of electrocatalysis due to their advantages such as high specific surface area,good electrical conductivity and easy adjustment.In this thesis,the transition metal was combined with carbon nanotube materials to prepare a bifunctional electrocatalyst with high catalytic activity and applied to zinc-air batteriesIn this thesis,different ratios of iron-nickel hydroxide nanosheets were grown on carbon cloth substrates by electrodeposition,and then heat-treated with dicyandiamide as carbon source at different temperatures.The iron-nickel nanosheets were gradually transformed into iron-nickel nanoparticles under under the carbothermally reductive atmosphere.At the same time,the iron-nickel hydroxide nanoparticles can catalyze the formation of carbon nanotubes by surrounding carbon species.Finally,the iron-nickel-Nanoparticle-Embedded N-doped Carbon Nanotube Arrays were prepared.The structure of the material were characterized by SEM,TEM,XRD and XPS.The results show that the length of carbon nanotubes is about a few microns and the diameter of the tubes is about 40-120 nm.The iron-nickel nanoparticles are evenly distributed in carbon nanotubes with a diameter of about 5-35 nm.Under the synergetic effect of iron-nickel bimetallic nanoparticles and N-doped carbon nanotubes,the performance of bimetallic nanoparticles is superior to single metal nanoparticles.In the oxygen evolution reaction,to reach a current density of 10 m A cm^-2,the Ni₂Fe₁@NCNT-800/CC electrode requires an overpotential of 232 m V.In the oxygen reduction reaction,the initial potential of the Ni₂Fe₁@NCNT-800/CC electrode was 0.94 V,the half-wave potential was 0.82 V and the limiting current density was 15.6 m A cm^-2.This shows that the Ni₂Fe₁@NCNT-800/CC electrode showed good catalytic performance in OER and ORR.The Ni₂Fe₁@NCNT-800/CC and Pt/C+Ir O₂ mixed catalysts were respectively assembled into an all-solid zinc-air battery and a liquid rechargeable zinc-air battery.The results showed that the Ni₂Fe₁@NCNT-800/CC electrode had better catalytic performance.It shows excellent stability in liquid rechargeable zinc-air batteries and can be stabilized for 300hours in charge-discharge cycles with a current density of 10 m A cm^-2.It shows excellent stability in liquid rechargeable zinc-air batteries and can be stabilized for 300 hours in charge-discharge cycles with a current density of 10 m A cm^-2.The good catalytic activity of Ni₂Fe₁@NCNT-800/CC is mainly due to the synergistic effect between iron-nickel nanoparticles and N-doped carbon nanotubes.