Controllable Preparation And Properties Of Iron/Nitrogen Co-Doped Multi-Stage Porous Carbon Coating Modified Zinc Anode

Zinc-air battery has attracted wide attention because of its high safety,large capacity,low cost and environmental friendliness.Among them,the design and development of cathode bifunctional catalyst for zinc-air battery has made breakthrough progress.At present,the research shows that the reversibility of zinc anode has become the key to determine the charging and discharging performance of zinc-air battery.However,zinc anode still faces serious challenges such as dendrite,deformation,passivation and hydrogen evolution corrosion,which directly hinders the practical application of reversible zinc-air battery.Therefore,the design and construction of highly reversible zinc anode is the key to solve the above problems.Using silica,ferrous sulfate and PQ-7 solution as templates,iron/nitrogen co-doped multilevel porous carbon materials were successfully prepared by high temperature calcination,and a composite zinc electrode modified by iron/nitrogen co-doped multilevel porous carbon was obtained by spraying technology.Subsequently,the prepared porous carbon materials and composite zinc electrodes were characterized by a series of physical spectra（including scanning electron microscope,transmission electron microscope,Raman spectrometer,X-ray diffractometer and X-ray spectrometer）and the electrochemical performance of symmetrical batteries（including chronopotentiometry and cyclic voltammetry）.Based on the above test results of micro-morphology,valence states of elements and electrochemical properties of the samples,the following conclusions can be obtained:（1）As a surface modification layer,the XPS and Mapping tests of Fe-N-MC coating show that the synergistic effect of pyridine nitrogen,pyrrole nitrogen and graphite nitrogen and the regulation of the electronegativity of zinc anode are beneficial to the uniform deposition of zinc ions,at the same time,it provides more adsorption sites for active zinc ions,reduces the local current density and improves the electric field distribution.In addition,Fe-N-MC coating can also inhibit dendrite growth and other side reactions by acting as zinc ion channels on the surface of zinc anode.The electrochemical test results show that the Fe-N-MC@Zn symmetrical battery exhibits a stable cycle life of more than 400 hours at a current density of10 m A cm^-2.In addition,at the current density of 5 m A cm^-2,the cycle life of zinc-air battery prepared with Fe-N-MC@Zn electrode as anode and Co₃O₄/Mn O₂/CNTs as catalyst was over500 hours.The above results show that the surface modification of zinc electrode by Fe-N-MC can improve its zinc affinity and reduce the energy consumption of ion desolvation and the energy barrier of zinc nucleation.More importantly,it can increase the number of ions on the electrode surface and form more effective zinc ion nucleation sites.（2）Based on the excellent electrochemical performance of the above-mentioned Fe-N-MC@Zn composite electrode,this paper further studies the thickness effect of the surface functional layer of the Fe-N-MC@Zn composite electrode.By changing the content of Fe-N-MC,Fe-N-MC@Zn composite electrodes with different thickness were successfully prepared.Among them,when the coating thickness is 20μm,the composite electrode shows the best cycle stability and reversibility in the symmetrical battery.The results show that when the content of Fe-N-MC is too low,the surface functional layer can not cover the surface of zinc electrode evenly,which leads to the high electric field intensity and the easy accumulation of zinc ions to form dendrites.When the content is too high,the coating formed is too dense,which makes the migration distance of zinc ions on the surface of zinc electrode increase and the steric hindrance increases,which leads to the increase of electrode overpotential.It is worth noting that in the zinc air test,the surface functional layer Fe-N-MC@Zn composite electrode with a thickness of 20μm shows a lower difference between charging and discharging voltages（only 0.8 V）and a higher peak power density(484.53 m W cm^-2).Above,the results show that the Fe-N-MC@Zn composite electrode prepared in this paper greatly improves the capacity and utilization rate of zinc anode,and has great potential for application in zinc-air batteries.（3）Based on the above,in order to combine the Fe-N-MC and the zinc electrode better,the Cu-Zn electrode was prepared by electrochemical deposition,and the surface was modified by Fe-N-MC to finally prepare the Cu-Zn-C electrode.In the performance test of symmetrical battery,the Cu-Zn-C electrode was stably cycled at a low overpotential of 0.04 V for more than300 hours,showing the reversibility far superior to bare zinc electrode and Cu-Zn electrode.In the rate performance test,the overpotential of the electrode was very low at all current densities,which indicated that the specific surface area of the zinc electrode was greatly improved after copper foam was modified with Fe-N-MC,and there were more zinc ion nucleation sites,thus showing good cycle stability.