Synthesis And Catalytic Actives Of Metal- Nitrogen-carbon-based Electrocatalysts

The purpose of this paper is to reduce the overpotential of oxygen reduction reaction?ORR?and improve the tolerance of catalysts,finally realize the long-term stable application of catalysts in zinc-air batteries.Herein,N-doped one-dimensional carbon nanofibers,two-dimensional graphene and three-dimensional porous carbon were respectively used to support transition metal oxide or nitride nanoparticles to obtain high-efficiency electrocatalysts with metal-nitrogen-carbon active sites.The influence of transition metal oxide or nitride nanoparticles on the improvement of electrochemical performance was investigated.The mechanisms of ORR catalytic process of composite catalysts were revealed.The following is the main research content of this paper:?1?Firstly,PAN/g-C₃N₄/FeCl₃ nanofiber membrane obtained by electrostatic spinning technology.Then,Fe₄N nanoparticles/one-dimensional nitrogen-doped porous carbon nanofiber composite?Fe₄N/N-CNFs?was synthesized through rapid calcining in vacuum of PAN/g-C₃N₄/FeCl₃.The lone pair electrons within g-C₃N₄ could bond with Fe³⁺,which was conducive to generate the Fe-N component.Then,Fe-N components were further converted into Fe₄N nanoparticles through“rapid calcining in vacuum”.The results showed that the ORR half-wave potential of Fe₄N/N-CNFs was higher than 20 wt%Pt/C 20 mV in 0.1 mol L^-1 KOH.In addition,the Fe₄N/N-CNFs-based zinc-air battery had a higher peak power density(135 mW cm^-2 vs.98 mW cm^-2)and better charge-discharge cycle life?55 h vs.7 h?than the 20 wt%Pt/C-based battery at 10 mA cm^-2.?2?CoO nanoparticles/two-dimensional nitrogen-doped graphene?CoO/NG?was successfully synthesized.g-C₃N₄ was partly decomposed into CO₃^2-and bonded with Co²⁺to generate CoCO₃ during hydrothermal process.Nitrogen element within undecomposed g-C₃N₄ was in situ doped into the carbon material during high temperature treatment.At the same time,CoCO₃ was decomposed and generated CoO and CO₂.CoO nanoparticles,as active components,were compound with nitrogen-doped graphene.CO₂ from the decomposition of CoCO₃ also evaporated to improve the specific surface area.Due to the presence of CoO nanoparticles and the synergistic effect between CoO and nitrogen-doped graphene,ORR half-wave potential of CoO/NG was only 4 mV lower than that of 20 wt%Pt/C,and the limited current density was significantly higher than that of 20 wt%Pt/C(6.46 mA cm^-2 vs.5.88 mA cm^-2).In addition,CoO/NG-based zinc-air battery could generate power density comparable to20 wt%Pt/C-based zinc-air battery(135 mW cm^-2 vs.91 mW cm^-2)and superior charge-discharge cycle life at 10 mA cm^-2?40 h vs.7 h?.?3?CoN nanoparticles/three-dimensional nitrogen-doped porous network carbon hybrid?CoN-NC?was synthesized with biomass gum?locust bean gum?as carbon source and guanidine carbonate as nitrogen source,respectively.Due to the hydrolysis of guanidine carbonate in water,resulting ammonium ions could coordinate with cobalt ions to form Co-?NH₂?₂,thereby dispersing cobalt metal and preventing them from aggregating.In the weakly alkaline aqueous solution formed by the dissolution of guanidine carbonate,galactose molecules were easy to react with mannose residue within locust bean gum through hydroxyl aldehyde condensation,which could increase carbon chain and further form hydrogel.The foam-like porous aerogel could then be formed by freezing-drying the hydrogel.CoN-NC with large specific surface area can be obtained by high temperature calcinated the aerogel.CoN-NC exhibited the same ORR half wave potential as 20 wt%Pt/C and significantly superior stability?initial current density drop value:1.8%vs.23.5%?.In addition,the CoN-NC-based zinc-air battery also demonstrated significant superiority over the 20 wt%Pt/C-based battery in charge-discharge cycle life at 5 mA cm^-2?115 h vs.28 h?.