Preparation Of Transition Metal Nitride Material Loaded On Carbon Fiber And Its Application In Zn-air Battery

Benefit from characteristics of Zn-air batteries（ZABs）and hydrogen fuel cells:high energy density,low cost and environment-friendly,they are more suitable for the development of the current society and have become very promising new energy.However,during the operation of ZABs,the electrochemical reaction kinetics of oxygen precipitation reaction（OER）and oxygen reduction reaction（ORR）are slow,which greatly reduce the performance of ZABs.In the development of hydrogen fuel cells,energy is wasted due to the high over potential of oxygen evolution reaction（OER）and hydrogen evolution reaction（HER）.As a new type of composite carbon material,transition metal doped carbon nanofibers have been favored by many researchers because of the synergistic effect between metal active substances and carbon nanofibers.The researches in this paper are as followed:The first work:we prepared nitrogen doped,single metal loaded nitrogen doped and bimetallic nitrogen doped carbon nanofibers by electrospinning technology.Through experiments,we found that the synthesized materials showed the best electrocatalytic properties when the materials were nitrogen doped and bimetallic loaded at the same time:tested in 1M KOH oxygen saturated electrolyte,the half wave potential of ORR was 0.86 V,and the over potentials of OER and HER at 10m A·cm^-2 current density were 388 m V and 249 m V,respectively.The performance results show that through the regulation of electron distribution by nitrogen doping,the defect degree of the material is increased,and the synergistic effect of bimetals ensures the performance of three-way catalysis.In addition,the application of the catalyst as the cathode catalyst of ZABs and the anode,cathode catalyst of electrolytic water showed excellent stability:the ZABs assembled with the catalyst as the cathode catalyst can continuously and stably circulate for 210 hours,and the application of the catalyst in electrolytic water can ensure a relatively stable catalytic reaction for 110hours at a current density of 10m A·cm^-2（the retention rate reaches 98.8%）.The second work:We used coaxial electrospinning technology to prepare non-metallic hollow porous carbon fiber materials.After noticing the limitations of the material of first experimental,we found that materials with larger specific surface area are profit for their better contact with the electrolyte,so that they generally show higher catalytic performance.Therefore,we designed and synthesized a hollow porous material to greatly increase the specific surface area of the material,thereby improving the performance of the catalytic material.The material showed a certain catalytic effect on ORR under alkaline conditions:half wave potential(E_1/2)of ORR was 0.81 V and limiting current density was 5.84 m A·cm^-2 in 0.1 M KOH oxygen saturated electrolyte.The application of the catalyst in the self-assembled zinc air battery showed excellent energy storage characteristics:the maximum power density during operation can reach 100 m W·cm^-2 at 178 m A·cm^-2 discharge current density.The third work:We used coaxial electrospinning technology to prepare transition metal doped hollow porous carbon fiber materials.After summarizing the previous two experimental experiences,we found that loading active substances on carrier materials with excellent conductivity and specific surface area can greatly improve the catalytic performance of materials.Therefore,we designed and synthesized an active material loaded on hollow porous carbon fiber materials to improve the performance of catalytic materials.The material showed a certain catalytic effect on ORR under acidic and alkaline conditions:it showed 0.89 V half wave potential(E_1/2)and 5.64 m A·cm^-2 limiting current density of ORR in 0.1 M KOH oxygen saturated electrolyte.Under the same conditions,the half wave potential of catalytic ORR is0.73 V in 0.1 M HCl O₄.The application of the catalyst in the self-assembled zinc air battery shows excellent energy storage characteristics:the maximum power density during operation can reach 172 m W·cm^-2,the specific capacity of the battery measured at a current density of 10 m A·cm-2 is as high as 904.5 m Ah·g _Zn^-1.