Preparation Of N,S Co-doped 2-D Mesoporous Carbon Catalysts And Their Application In Electrocatalysis

The rapid development of today’s society cannot be separated from the continuous supply of energy.The development of clean energy can effectively avoid the problems of energy exhaustion and environmental deterioration.In recent years,the exploration of low-cost and efficient clean energy electrochemical conversion and storage technology has become a hot spot because of the defects of clean energy itself,such as volatility and geographical limitations.However,the slow cathodic kinetics rate restricts the large-scale application of electrochemical conversion and chemical storage devices.Electrocatalysis has been widely studied as a basic science to solve this problem.Among many electrocatalysts,carbon materials with excellent electrical conductivity and strong corrosion resistance have great application potential.In order to give full play to the greatest advantages of carbon materials,a series of electrocatalysts with excellent catalytic activity of oxygen reduction were constructed from the construction of two-dimensional mesoporous carbon materials,through the hetero-atomic co-doping of nitrogen（N）and sulfur（S）and the loading of Pt（Pt）ultramicro subnano particles to control the active sites of mesoporous carbon nanosheets.The morphology,structure,electrochemical properties and oxygen reduction reaction path of the catalyst were investigated.Specifically carry out the following research contents:（1）Mesoporous carbon nanosheets were fabricated on Na Cl salt template surfaces via a surface co-assembly strategy using lab-made high molecular weight biblock copolymer PEO₁₁₃-b-PS₂₄₀ as template agent with Resol as carbon source.A series of MCS-NS-X catalysts doped with nitrogen and sulfur diatoms at 800°C,900°C and1000°C were prepared by thiourea evaporation method.The optimal preparation temperature of nitrogen-sulfur co-doping in mesoporous carbon nanosheets was studied.The results show that the catalyst prepared at 900°C has the highest nitrogen and sulfur doping content,nitrogen content is 4.13 at.%,sulfur content is 2.30 at.%,the initial potential and half wave potential of oxygen reduction reaction under alkaline conditions are 0.93 V and 0.83 V,respectively.The average electron transfer number in oxygen reduction reaction is 3.85.The catalyst prepared at 900°C was applied to the zinc-air battery.The battery was charged and discharged stably for more than 200 cycles at 5m A cm^-2,and the voltage efficiency was 46%.（2）Pt nanoparticles were deposited on the surface of mesoporous carbon nanosheets with different nitrogen and sulfur doping content,which prepared at different temperatures as substrates by ALD.HRTEM,EDS and X-ray photoelectron spectroscopy（XPS）confirmed the successful deposition of Pt ultrafine subnano particles with a particle size less than 1 nm,showing that the content of Pt atoms accounted for about 8.35 at.%after 20 cycles of deposition.The catalysts supported on900°C nitrogen-doped mesoporous carbon nanosheets showed excellent catalytic performance for oxygen reduction under both acid and alkaline conditions.Especially under alkaline condition,the half-wave potential（0.83 V,vs.RHE）and limiting current density(5.89 m A cm^-2)of the catalyst are similar to those of the commercial Pt/C catalyst.The half-wave potential and limiting current density of the catalyst under acidic condition are 0.77 V and 5.91 m A cm^-2,respectively.At the same time,the catalyst has stable methanol oxidation resistance and cycle stability.After 4000 acidic cycle aging,it still maintains the same initial potential and half-wave potential as the initial one.After analyzing the catalytic mechanism of nitrogen-sulfur co-doped mesoporous carbon nanosheets loaded with Pt subnanoparticles,it was found that the electrochemical performance of the catalyst was related to the content of nitrogen and sulfur in the substrate material.A large amount of doping resulted in the existence of Pt subnanoparticles in the oxidation state with low electron density,leading to a high catalytic activity.In summary,in this paper,nitrogen and sulfur co-doped two-dimensional mesoporous carbon electrocatalysts with excellent electrocatalytic oxygen reduction performance were prepared based on the co-assembly and thiourea evaporation two-step method,which has potential application in zinc air batteries.On this basis,the Pt subnanoparticles modified N,S co-doped two-dimensional mesoporous carbon electrocatalyst was obtained by ALD method.It has excellent catalytic activity of oxygen reduction in acid and alkaline conditions,and has the cycling stability of Pt series catalyst which is rare.The above research has certain research value for the modification and application of carbon based electrocatalyst for oxygen reduction.