| Zinc-air batteries have been widely valued for their high energy density,high safety and abundant resources.However,the synthesis of highly efficient non-noble metal electrocatalysts and serious polarization of air cathodes is an urgent and challenging task to promote the application of zinc-air batteries.Therefore,this work mainly starts from two aspects of improving the activity and stability of catalyst and optimizing the preparation process of air cathode,the key of which is to compare and analyze relevant parameters to improve the discharge performance of air cathode.Firstly,a simple one-step pyrolysis method was used to prepare three-dimensional porous Co@Co-NPC by doping heteroatomic P into the Co,N co-doped porous carbon catalysts（Co-N-C）derived from the flower-like bimetal（Co/Zn）metal-organic framework（MOFs）during carbonization.Co-N-C material was modified by changing the doping amount of P.Through physical characterization and electrochemical tests such as rotating disk electrode system,it was found that the obtained 3D-Co@Co-NPC-6 had good methanol tolerance and cycling stability when the doping amount of P was 0.5%,which was superior to the commercial Pt/C catalyst.In addition,its half-wave potential was 0.872 V and the limiting diffusion current density was 4.78 mA cm-2.The doping of P also makes a great contribution to the improvement of oxygen evolution reaction activity,indicating that doping of heteroatomic P can effectively improve the activity and stability of Co-N-C catalyst.When 3D-Co@Co-NPC was used as the catalyst to assemble the zinc air battery,the open circuit potential was 1.486 V,the power density was 182.5 mW cm-2,and the capacity was 764 mAh g Zn-1.The charging-discharging cycle test had excellent stability（over 90 h）,which proved the potential application possibility of the catalyst in the zinc-air battery.Acid washing experiments showed that Co nanoparticles could promote the enhancement of3D-Co@Co-NPC-6 catalytic activity.3D-Co@Co-NPC-6 has excellent electrocatalytic activity,which is mainly attributed to the high percentage of pyridine nitrogen and graphite nitrogen,three-dimensional porous structure and high electrical conductivity after P doping.Secondly,the structure of the air cathode current collecting layer was optimized.The conductive carbon powder and Polytetrafluoroethylene（PTFE）emulsion were filled in the current collecting layer for hydrophobic treatment.The biggest influencing factor of PTFE in the preparation process of the air cathode was determined by orthogonal experiment.The results show that the air cathode 3-300 exhibits excellentelectrochemical performance when PTFE content is 3.6 times the mass of acetylene black and the heat treatment temperature is 300℃.A moderate amount of PTFE ensures a balance between the number of small and large pores.Heat treatment at 300℃ can improve the fluidity of softened PTFE and make the air cathodes have uniform hydrophobicity.The polarization potential of air cathode 3-300 at 100 mA cm-2 is-0.405 V vs.Hg/HgO,indicating that the air cathode 3-300 has relatively small polarization loss.After the stepwise constant current discharge of 5-20 mA cm-2,the voltage retention rate is 94.47%,indicating that the air cathode 3-300 has excellent multiplier performance. |
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