Iron-based Transition Metal-based Nitrogen-doped Carbon Materials For Electrocatalytic Oxygen Reduction Reactions

With the continuous development of society,the traditional fossil energy such as coal,oil and natural gas is increasingly exhausted,so the development and utilization of sustainable clean energy has become the current research hotspot.Zn-air battery(ZAB)is considered to be one of the most efficient energy devices because of their high efficiency,high power density and environmental friendliness.Oxygen reduction reaction(ORR)is the discharge reaction of ZAB,and its slow kinetic process plays a decisive role in the performance of the whole device.At present,precious metal Pt has been considered as an ideal electrocatalyst for ORR,but its high cost,scarce resource and poor durability greatly limit commercial application.Therefore,it is very important to develop non-precious metal-based ORR electrocatalysts with low cost and excellent performance.In view of this,in this paper,iron-based transition metal and nitrogen-doped carbon composites were prepared by the coordination and complexation of metal ions with nitrogen-containing carbon source,and their ORR performance and catalytic mechanism were further explored.The main research contents are as follows:1.Fe₃C/N-doped carbon nanosheets(Fe₃C-FeN/NC)containing single atoms Fewere prepared by complexing the nitrogen-containing groups in chitin with Fe³⁺and Zn²⁺combied with thermal decomposition and acid treatment.The synergistic effect between Fe₃C nanoparticles and single atoms Femakes an excellent ORR catalytic activity.The carbon coated nanostructure avoids the dissolution of Fe₃C during the electrochemical test,improving the stability of the catalyst.Density functional theory(DFT)was used to identity the active sites and catalytic mechanism of ORR.As for air-cathode,the assembled primaty ZAB exhibited a discharge time of 88 h and a specific capacity of 745 mA h g^-1 at 10 mA cm^-2,which was much better than commercial Pt/C catalyst.2.Bamboo-like N-doped carbon nanotubes embedded with Co particles were prepared by the coordination of nitrogen-containing groups in dicyandiamide with Co²⁺and Zn²⁺ions combined with freeze-drying and pyrolysis.The existence of carbon nanotubes was conducive to electron transport,and the synergistic effect between Co particles and bamboo like nitrogen doped carbon nanotubes resulted in an excellent ORR catalytic activity.As a result,the primary ZAB showed a discharge time of 82 h and a specific capacity of 783 mAh g^-1 at 10 mA cm^-2,overperforming than commercial Pt/C catalyst.3.The FeCo alloy nanocomposites coated with nitrogen-doped carbon nanotubes was prepared by coordinating the nitrogen-containing groups in dicyandiamide with Fe³⁺and Co²⁺ions.The synergistic effect between FeCo alloy nanoparticles and nitrogen doped carbon nanotubes could enhance ORR activity,while the carbon coated nanostructures improved the stability of the catalyst.Therefore,the primary ZAB exhibited a discharge time of 120 h and a discharge capacity of 765 mAh g^-1 at 10 mA cm^-2,which is superior to commercial Pt/C catalyst.