Construction Of N-doped Carbon Nanofiber Catalysts For Zn-air Batteries And Charge-discharge Performances Investigation

Zn-air batteries are regarded as next generation energy conversion and storage devices with commercial prospects.Therefore,constructing non-precious metal catalysts with the advantages of low-cost,high catalytic activity and excellent stability to catalyze the sluggish oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)which occur in the cathode of Zn-air batteries is very critical.While the development of flexible electronic devices has put forward higher requirements for the design of catalysts of Zn-air batteries.Electrospinging technology was utilized in this investigation to prepare nitrogen-doped hierarchical porous carbon nanofibersas as self-stading electrode for primary liquid-state and flexible Zn-air batteries.And NiCo bi-metal doped porous carbon nanofibers are designed as cathode catalysts for rechargeable liquid-state and quasi-solid-state Zn-air batteries.In addition,in long cycles,the charge and discharge performance of Zn-air baterries damp and further influence the cycling stability.Therefore,the modifications of Zn anode and electrolyte were employed to improve the long cycle stability of Zn-air batteries.Finally,the hydrogel electrolyte of flexible Zn-air batteries was discussed and its effect on charge-discharge performance was investigated.The specific research contents are as follows:(1)In situ ZnO activation coupled electrospinning strategy was developed to facilely fabricate N-doped porous carbon nanofibers(NPCNFs)as a self-standing electrode for flexible Zn-air batteries.The in situ activation of ZnO on the surface of carbon nanofibers not only enhance the defect level of carbon structure,but also increase the specific surface area and the ratio of edge pyridinic-N.These factors together promote ORR electrocatalytic performance of NPCNFs,which exhibit ORR onset potential of0.95 V and half-wave potential of 0.85 V in 0.1 M KOH electrolyte.Liquid-state Zn-air battery with NPCNFs as cathode catalyst exhibits exceptional power density of 84.02 m W/cm~2,favorable discharge voltage of 1.22 V and discharge stability at 5 m A/cm~2.Finally,the flexible Zn-air batteries with NPCNFs as self-standing electrode possess the stability of discharge under bending at different angles.(2)Bi-metal NiCo doped 1D PAN/PVP complexed nanofibers were sythesised by electrospinning technology.The doped of bi-metal NiCo not only enhances the degree of graphitization of carbon structure and increases the content of pyridinic-N and graphitic-N,which improve the catalytic performance and stability of NiCo/CNFs toward ORR,but also forms more metal oxide species with higher valance to enhance the catalytic activity of NiCo/CNFs in OER.The electrochemical test results show that NiCo/CNFs has the OER potential of 1.68 V at 10 m A/cm~2 and ORR half-potential of 0.78V,which possesses good bifunctional catalytic activities.Moreover,rechargeable Zn-air batteries with NiCo/CNFs as cathode catalyst has charge voltage of the first ciruit at 5 m A/cm~2 of 2.05 V and discharge voltage of 1.15 V,which exhibit wonderful charge and discharge performance.Finally,NiCo/CNFs is applied to the flexible Zn-air batteries,showing good charge-discharge performance and maintaining stability within 15 h.(3)The modifications of Zn anode and electrolyte are employed to solve the problem that the charge and discharge performance of Zn-air batteries decrease in long circulation.Nano-granulation treatment on the surface of Zn anode increases the contact area between Zn and electrolyte,which improves the contact interface.EDTA as an organic addition is added into electrolyte for electrolyte modifaction.This method influences the electrochemical behavior of Zn during deposition and reduces the deposition particle.These two modification methods both improve the charge-discharge performance and stability in long-cycle charge discharge of Zn-air batteries.Moreover,the water retention rate,ionic conductivity and electrochemical stability of hydrogel electrolyte were discussed to investigate its influence in charge-discharge process.