Preparation And Electrocatalytic Performance Of Perovskite/Nitrogen Doped Carbon Composites

The lack of high-efficiency,stable and low-cost bifunctional electrocatalysts is one of the main factors hindering the commercial application of zinc-air batteries.Perovskite-type oxides have become potential catalyst candidates due to the tunability of their lattice structure and the flexibility of electronic configurations.However,pure perovskites have small specific surface areas,low electrical conductivity,and easy agglomeration between particles.The oxygen deficiency concentration is not high,and its inherent activity still cannot meet people’s needs.Based on this,this thesis modified it by combining with N-doped carbon materials and preparing porous perovskites to obtain electrocatalysts with excellent bifunctional catalytic activity.The main contents are as follows:Using lamellar graphite phase carbon nitride as the carbon source and nitrogen source,a series of LaCo_0.7Fe_0.3O₃/N-doped carbon composite materials with different N-doped carbon ratios（LCFO/NC,LCFO/2NC,2LCFO/NC）.The phase structure and morphology of the catalysts were characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM）and transmission electron microscopy（TEM）.The bifunctional catalytic activity（ORR/OER）of the samples was evaluated using a rotating disk electrode,which was used as an air electrode to assemble a zinc-air battery,and the performance of the battery was tested by a constant current charge-discharge instrument.The results show that when the mass ratio of LCFO to N-doped carbon is 2:1,that is,2LCFO/NC has the highest electrocatalytic activity.Finally,through density functional theory（DFT）calculations,the underlying reasons for the improved electrocatalytic performance are analyzed and discussed.Porous LaCo_0.7Fe_0.3O₃ with different pore sizes and quantities was prepared by adjusting the size and proportion of SiO₂ microspheres template by hard template method.XRD analysis showed that the SiO₂ template can be successfully removed by Na OH washing without affecting the crystal structure of the perovskite.Observed by SEM,when the size of SiO₂ microspheres is 280 nm and the mass ratio of LCFO to SiO₂ is 1:2,PLCFO（2Si-280）has a uniform and abundant mesoporous structure.At the same time,PLCFO（2Si-280）also showed the best electrocatalytic performance in the electrochemical test.Then PLCFO（2Si-280）was mechanically mixed with N-doped carbon to prepare2PLCFO/NC,and the electrocatalytic activity was further improved.In the ORR process,the diffusion limiting current density reached 5.6 m A cm^-2,which was significantly greater than PLCFO（2Si-280）(5.2 m A cm^-2),the OER overpotential is 470 m V when the current density is 10 m A cm^-2,which is smaller than that of PLCFO（2Si-280）（490 m V）.Simultaneously,2PLCFO/NC exhibits excellent durability,the current density attenuation is only 8.6%after 8 hours of operation.