Construction Of Defect Carbon Electrocatalysts And Its Application In ORR Reaction

The consumption of fossil energy and environmental pollution bring great serious.In order to slow down the growth of this series problems,clean energy is urgent to develop.Metal-air batteries and proton membrane fuel cells can be used as promising alternatives to fossil energy sources.Oxygen reduction reaction（ORR）is the core of the electrochemical conversion process.The electrocatalysts activity determines the overall performance and efficiency of related devices.At present,the platinum-based catalysts used as traditional commercial electrocatalysts have high reactivity,however the poor cycle stability,low resources and high costs hinder their wide application.Therefore,it is great significance to develop new energy conversion technologies.Carbon nanomaterials are widely used in electrochemical research due to their advantages of high conductivity,good stability,and low costs.Recent studies have shown that defect sites are highly potential ORR catalytic active centers in carbon-based materials.However,how to introduce abundant defects into carbon materials to improve the catalytic activity is still a big challenge.This work focuses on the construction of defect-based carbon materials and its ORR catalytic activity as well as its performance in Zn-air battery.Firstly,the coordination polymer[Zn（ptt）₂]as precursor was synthesized by reacting zinc nitrate hexahydrate and 1-Phenyl-1H-tetrazole-5-thiol（hptt）.Then,a series of defect-based carbon materials have been obtained by adjusting the temperature of the pyrolysis of[Zn（ptt）₂].As the temperature increased,the size and content of zinc sulfide particles gradually decreased,the degree of denitrification and defect density gradually increased.Electrocatalyst C1100 with defects（I_D/I_G=1.05）,co-doping of nitrogen and sulfur and nano-Zn S,was successfully obtained which showed high ORR electrocatalysis in alkaline medium.The half-wave potential（0.894 V）of C1100 is 37m V higher than that of 20%Pt-C.After 10 hours test,the cathodic current of C1100retained 94.5%of its baseline current,it also has a good methanol tolerance.The current density of cathode C1100 is 265 m A/cm²,and the peak power density is 134m W/cm²,both of which are superior to 20%Pt-C（the current density of 20%162m A/cm²and the peak power density is 83 m W/cm²）.When discharged at 10 m A,the ZAB delivers no obvious decrease of voltage in long-term discharge.In order to reveal the source of defective active centers in the catalyst,the samples obtained by carbonization at 800℃and 900℃were subjected to secondary carbonization at 1100℃before and after pickling Zn S.In comparison,in carbonization process the presence of Zn S can help to increase the carbon defect,and the electrocatalytic research showed that the increase of carbon defect is beneficial to improve the ORR performance.In general,the carbothermal reaction of Zn S can produce carbon defects on the carbon material while obtaining small-scale Zn S,which are conducive to the improvement of its catalytic activity.