Preparation And Electrochemical Performance Study Of Metal-N-C Materials For Zinc-Air Batteries

Zinc-air batteries offer a promising application prospect due to their highly-safety,environment friendliness,high energy conversion rate and energy density.Nonetheless,their large-scale application is hampered by the sluggish kinetics of oxygen reduction reaction（ORR）and oxygen evolution reaction（OER）.To date,precious metal catalysts,such as Pt,RuO₂,IrO₂,have achieved improved catalytic performance in the above two reactions,but their commercial application has been impeded by their high-cost,limited catalytic function,and poor stability.It is,therefore,of paramount importance to develop bifunctional electrocatalysts with high activity,long durability and low cost for the development of zinc-air batteries.Here,metal-nitrogen-carbon electrocatalytic materials were investigated to improve the activities of ORR and OER by modulating the material components and structures.The contents of the study are organized as follows in this thesis:（1）Preparation and electrochemical performance study of Co-N-C nanowire:The solvothermal reaction was used to create the one-dimensional cobalt nanowire skeleton,following that,a double-layer hollow Co-N-C nanowire can be obtained using carbon-coating strategy under the hydrothermal co-precipitation condition.After optimizing the carbon coating process and heat-temperature treatment,the Co,N-doped carbon nanowires（NTC-Co@GLC-700）pyrolyzed at 700℃shows a promising electrocatalytic performance for ORR,with a half-wave potential of 0.80 V vs.RHE.Furthermore,its overpotential of 370 m V towards OER at 10 m A cm^-2is comparable to commercial RuO₂catalyst.（2）Preparation and electrochemical performance investigation of fishnet-like Co-N-C materials:this subsection is dedicated to the optimization of preparation methods and material components in order to improve the electrocatalytic activity and stability of bifunctional Co-N-C materials.The fishnet-like Co,N-doped carbon composite（Co MT-IPA-900）was synthesized controllably via solvothermal reaction with the following pyrolysis step,The effects of carbon source,nitrogen source and solvent on the morphology and electrochemical properties were investigated.The prepared Co MT-IPA-900 demonstrated excellent electrochemical performance in alkaline electrolyte,with a half-wave potential of 0.86 V vs.RHE for ORR,which is comparable to that of 20wt.%Pt/C.When compared with commercial RuO₂,it also has a comparable overpotential towards the OER at 10 m A cm^-2.（3）Preparation and electrochemical performance study of flake Co Fe alloy/M-N-C materials:In this section,Co,Fe is introduced to synthesize the Co Fe alloy/metal-N-C material（TA-Co Fe-900）via co-pyrolysis with the controllable temperature.The optimized TA-Co Fe-900 exhibits bifunctional catalytic activity comparable to that of noble metal catalysts in alkaline electrolytes,with a half-wave potential of 0.89 V vs.RHE for ORR and overpotential of 405 m V at 10m A cm^-2for OER.Furthermore,when used in the secondary zinc-air battery,the TA-Co Fe-900 catalyst presents a high durability with charged/discharged cycles for 100 hours at a current density of 5 m A cm^-2.