Preparation Of One And Dual Transition Metal Atom Catalysts And Application In Oxygen Reduction Reaction

With the development of human society,great increase of global energy demand and large use of fossil energy will lead to environmental pollution and the exhaustion of fossil energy.Under the circumstances of global environmental pollution and energy crisis,green and sustainable energy technologies are great desired,metal fuel cells and hydrogen-oxygen fuel cells are effective energy storage conversion technologies compared to wind,photovoltaic,hydrogen,ocean,biomass,geothermal,and nuclear energy due to its advantages of low-cost and clean.metal fuel cells and hydrogen-oxygen fuel cells involve a series of electrochemical processes,mainly including oxygen reduction reaction（ORR）,hydrogen evolution reaction（HER）,and oxygen evolution reaction（OER）and hydrogen oxidation reaction（HOR）.Particularly,ORR is the most important reaction during discharge step of fuel cells.At present,these energy technologies suffer from low reactive efficiency,exploring effective electrocatalyst is a key strategy to solve the problem.Commercial Pt/C is the best catalyst for ORR but hindered by high-cost,methanol and carbon monoxide poisoning of Pt,resulting in the low energy efficiency and commercialization of fuel cells are ultimately limited.Therefore,development of low-cost and efficient transition metal-based catalyst is a significant goal.In recent years,single atomic catalysts（SACs）composed by transition metals as active sites have been widely studied in oxygen reduction catalysts because of their chemical stability,strong conductivity and low-cost.In the carbon based SACs,nitrogen contained polymers are the common carbon precursors.The nitrogen doped into carbon facilitates the anchoring of transition metal single atoms via forming matel-nitrogen structures,which creates abundant highly coordinative unsaturated catalytic active sites,thus the loading of metals can be obviously decreased and catalytic activity can be greatly improved at the meanwhile.Inspired by above discussion,we utilized liquid acrylonitrile oligomer（LPAN）as preecusor to synthesized a series of transition metal based SACs for ORR.Then summarized the ORR performances of above SAC,and selected appropriate two transition metal elements as a couple by the principle of complement each other’s advantages to design a dual atom catalyst（DAC）,eventually fulfilled the aim of further improve the ORR activity.（1）Utilizing liquid acrylonitrile oligomer（LPAN）,transition metal chlorate and commodity conductive carbon black（Ketjenblack EC-300J）as precursor,we synthesized a series of SACs（M/N/C,M=Fe,Mn,Co and Ni）by simple pyrolysis and acid treatment.The ORR performances of above SACs were investigated,and the Fe/N/C and Mn/N/C catalyst exhibit the highest catalytic current density and half-wave potential respectively.（2）Based on above conclusion,we further synthesized dual atomic catalyst composed of Mn and Fe（Mn Fe/N/C）by the same preparation method to fulfill the complement advantages of Mn and Fe sites.The synergistic effect between Mn and Fe verified by the X-ray absorption spectroscopy（XAFS）has positive effect toward ORR catalytic activity,rendering Mn Fe/N/C exhibits excellent ORR performances with ultra-high onset potential of 1.02 V,half-wave potential of 0.900 V and limit current density of 6.147 m A cm^-2,which not only better than the parents of Fe/N/C and Mn/N/C,but also surpass Pt/C.Eventually,Mn Fe/N/C was used as cathode catalyst for Zinc-air battery,and the power density,specific capacity and durability of the Zinc-air battery achieved remarkably improved.