Defect Engineering Of Metal-free Oxygen Reduction Catalyst And Application In Zinc Air Battery

The development of oxygen reduction catalysts is the key of renewable energy technologies such as proton membrance fuel cells and zinc-air batteries that are used for energy conversion and storage.However,this reaction process involves a multi-step proton coupling and electron transfer process,and its slow kinetics limits the choice of oxygen electrocatalysts,so that Pt and its alloys are still the best ORR catalysts at present.However,in addition to the problems of high price and scarcity of resources,Pt-based catalysts still face problems such as poor stability and tolerance to methanol,which limits their possibilities for large-scale industrial applications.Therefore,the development of efficient,stable and economical oxygen electrocatalysts is the main challenge currently.In recent years,carbon nanomaterials have been studied as the main choice of oxygen electrocatalyst materials,which have many advantages,such as low cost,high electrical conductivity,and environmental friendliness.More importantly,carbon nanomaterials usually show excellent stability and methanol resistance,which makes it easier to adapt to complex battery working environments.However,carbon nanomaterials often show low-profile catalytic activity,how to improve their oxygen reduction catalytic activity is the focus of current research.In this paper,we have prepared a defect-rich three-dimensional（3D）mesoporous carbon nanomaterial,using zinc oxide quantum dots as a high-temperature oxygen supply agent and a carbon consumable,and performing a carbon-thermal reduction reaction through high-temperature heat treatment.In engineering,carbon defects were constructed in situ on the carbon surface as active sites for oxygen reduction.The resulting defect-rich three-dimensional mesoporous carbon nanomaterials and ordered mesoporous carbon CMK-3 have significantly improved the oxygen reduction catalytic activity.Its extended application to zinc-air batteries also shows high power density and stability.The specific work is as follows:Taking a typical three-dimensional（3D）ordered mesoporous carbon nanomaterial（CMK-3）as a good carbon matrix,using Zn O quantum dots（QDs）with ultra-high specific surface area as high-temperature oxygen supplyier Aand carbon depleting agent,we can obtain the material CMK-3@QDs-900 by dispersing Zn O QDs uniformly on the surface of CMK-3 ordered channels.Taking nitrogen as the protective gas,after high-temperature heat treatment,using Zn O QDs,a vigorous carbothermal reduction reaction Zn O（s）+C（s）=Zn（g）+CO（g）takes place to produce rich carbon defects.Then,the defect-rich mesoporous carbon nanomaterials CMK-3@qds-900 is obtained,and the original three-dimensional morphology and mesoporous channels of CMK-3are well preserved.The half wave potential of the material is 0.903 v（V vs RHE）in0.1M KOH electrolyte and 0.769 v（V vs RHE）in 0.1M HCl O₄electrolyte.CMK-3@QDs-900 catalyst showed excellent stability after 100-hour I-T test in alkaline medium,and the current density only decreased by 5.6%.In addition,CMK-3@QDs-900 is used as a cathode catalyst in self-assembled zinc air batteries,exhibiting high power density(203 m W cm^-2;～125%of 20%Pt/C)and good stability.