The Preparation And Oxygen Reduction Reaction Performance Of Carbon Materials Derived From Formamide

Metal-air batteries as a new electrochemical energy storage device have been widely concerned by researchers due to their high theoretical energy density and environmental friendliness.However,the sluggish kinetic rate of the oxygen reduction reaction（Oxygen Reduction Reaction,ORR）at the air cathode severely limits its large-scale commercial application.Although noble metal Pt-based catalysts and their alloys have been widely reported owing to their excellent catalytic performance,they also have the disadvantages of scarce resources,high cost and poor stability.Therefore,it is very necessary to explore low-cost and high-activity non-noble metal electrocatalysts for the development of metal-air batteries.In this project,inexpensive and low-toxic formamide was used as carbon and nitrogen sources,which could undergo the Schiff-base condensation reaction to form poly-formamide and chelate free metal ions under solvothermal conditions.Carbon materials with excellent ORR activity could be obtained after the subsequent high temperature pyrolysis.The research contents mainly include the following aspects:（1）Pyridine-N is generally considered as the the main active sites in N/C materials.In view of the low pyridine nitrogen content of the reported N/C materials,benzamide and Zn²⁺are introduced to participate in the condensation of formamide to construct poly-formamide-benzamide precursors.Benzamide as additional ligands can anchor Zn²⁺with formamide to form a nitrogen-rich precursor.Then N/C materials with high pyridine nitrogen content were obtained after the volatilization of Zn during the subsequent pyrolysis.The study found that the pyridine-N content of the materials could be effectively promoted by regulating the amount of benzamide.The catalyst with the highest pyridine-N doping content（about 8.93 at%）exhibited excellent ORR performance in 0.1 M KOH solution with a half-wave potential of 0.857V（vs.RHE）.（2）Aiming at the problem that it is difficult to increase the metal Fe loading due to the thermodynamic instability of Fe atoms.On the basis of（1）,Fe²⁺is further introduced and anchored to forms high metal loading precursor due to the strong metal chelating ability of formamide and benzamide.The anchored Zn²⁺during high-temperature pyrolysis could act as an effective space fence to inhibit the agglomeration of Fe atoms,and finally Fe-N/C catalyst with high Fe loading was obtained.Compared with the material without benzamide,the metal loading in the Fe-N/C material after the introduction of benzamide was nearly doubled（about6.52 wt%）.It exhibited outstanding ORR activity in 0.1 M KOH solution with a half-wave potential of 0.878 V（vs.RHE）.（3）To solve the limitation that O-containing intermediates are difficult to desorb due to their strong binding on the Fe-N_x site,we introduce the Fe₃C nanoparticles with electron donating property to optimize the electronic structure of the Fe center.Fe³⁺and Zn²⁺are introduced to participate in the condensation of formamide.The condensation of Zn²⁺and formamide will form the Zn-N coordination structure,while Fe³⁺will not only form the poly-formamide with Fe-N coordination,but also form the Fe-C coordination of metal cyanide Zn₂Fe（CN）₆due to its oxidizing property.Using the poly-formamide and Zn₂Fe（CN）₆ as effective templates for Fe-N_x and Fe₃C species respectively,Fe-N/C catalysts with Fe₃C@C core-shell structure were obtained after pyrolysis.Benefiting from the synergistic effect of Fe-N_xand Fe₃C nanoparticles,the catalyst exhibited excellent ORR activity with a half-wave potential of 0.895 V（vs.RHE）in 0.1 M KOH solution.