Study On Modification Of Co-N-C Oxygen Reduction Catalyst In Acid System

Fossil energy,as the main source of energy in the world today,is an important driving force for social and economic development,but due to its non-renewable and polluting emissions,it has caused global concerns about energy shortage and climate change.Compared with traditional fossil fuels,metal-air batteries,fuel cells and other electrochemical conversion and energy storage technologies have many advantages.However,the widespread application of these technologies must overcome the slow kinetic cathodic oxygen reduction reaction?ORR?,which is inseparable from highefficiency,low-toxic,low-cost and green sustainable catalysts.Atomic-scale dispersed active site catalysts,whose fully exposed atoms can increase the number of active sites;the low coordination unsaturated state and the enhanced metal carrier interaction can improve the intrinsic activity of the active site,the synergistic promotion of these two aspects is conducive to improving The performance of the catalyst.Because of its weak Fenton reaction,the atomically dispersed Co-N-C catalyst is the best choice to replace the Fe-N-C catalyst with the best performance in acidic systems.However,Co-N-C catalysts face two major challenges: 1)lower intrinsic activity;2)high H2O2 yield,which greatly restricts its practical application.In response to the above problems,the work of this paper takes Co-N-C catalyst as the research object,by introducing other metal elements in Co-N-C catalyst to compensate its lower intrinsic activity and reduce H2O2 yield.The research work mainly focuses on the following two aspects:1.Design and synthesis of Co-N-C@Pt NPs catalyst.Pt is the most effective catalyst for ORR,so a small amount of Pt can be used to compensate for the low activity of Co-N-C catalyst.This paper developed a method for introducing Pt into Co-N-C catalysts without destroying highly active atomically dispersed Co sites.Synchrotron radiation characterization confirmed that the synthesis of Co-N-C@Pt NPs retains most of the atomically dispersed Co sites in Co-N-C,and these Co sites are the main part of Co-N-C@Pt NPs.Provides the main catalytic site for the catalyst.In addition,spherical aberration electron microscopy showed that more micropores appeared in Co-N-C@Pt NPs,indicating that the formation of Pt Co alloy analogs promoted the formation of a porous structure,which caused some of the main body-supported CoN₄ sites to be edgesupported CoN₄ sites.Point,this is conducive to better oxygen adsorption.The designed and synthesized catalyst exhibits excellent ORR performance.The acidic half-wave potential is superior to commercial Pt/C,and the H2O2 yield is significantly reduced.2.Design and synthesis of?Co,Mn?-N-C catalyst.In order to further reduce the cost of the catalyst,this paper introduced Mn as an additional active site into the Co-NC catalyst.First,by controlling different Co content and methanol content,the Co-N-C catalyst with the best performance was selected.Based on the Co-N-C,Mn is introduced,and the content of the introduced Mn is controlled to select the best?Co,Mn?-N-C catalyst.Electrochemical experiments show that the introduction of an appropriate amount of Mn can improve the ORR performance of the catalyst.This is due to the presence of additional N sites in the Co-N-C matrix to anchor Mn to form atomically dispersed MnN₄ sites.These Mn sites provide additional activity center.However,the introduction of excess Mn will be detrimental to the catalytic activity,because the introduction of excessive Mn will cause a large number of clusters in the catalyst,which is not conducive to the improvement of the catalyst activity.