Preparation And Electrocatalytic Performance Of Non-noble Metal Carbon Materials Derived From Polydopamine

Rechargeable Zn-air batteries（ZABs）have been considered as the next generation of energy conversion and storage devices because of high theoretical energy density,good safety and environmental friendliness.Nevertheless,the sluggish kinetics and high overpotential of oxygen reduction reaction（ORR）and oxygen evolution reaction（OER）during the discharge and charge process at the air cathode hindered the practical application of ZABs.High cost and scarcity of noble metal catalysts（Pt/C,Ru O₂ and Ir O₂ etc.）involving air cathode of ZABs further restrict their large-scale commercialization and developments.These has encouraged researchers to explore cost-effective,excellent performances,stabilities and bifunctional non-noble metal electrocatalysts.It is still a challenge to design and regulate non-noble metal catalysts to achieve the excellent performance of noble metal catalysts.The size and morphology of the non-noble metal template synthesized by hydrothermal method can be controlled.When dopamine is oxidized and polymerized on its surface,the metal template not only plays a supporting role,but also provides a metal active center.Polydopamine can be complexed with a variety of metals,anchor the metal into a single atom or cluster,after carbonization can be completely replicated template morphology.In addition,studies have shown that the carbonization yield of polydopamine is high and easy to form amorphous carbon.Through this method,a variety of oxygen electrocatalysts derived from metal templates can be prepared.In this thesis a variety of catalysts are prepared and designed based on this method,and the best performance is applied to the assembly and testing of ZABs.Specific research contents are as follows:（1）Preparation of Fe-Co synergistic dual-single atom carbon nanotubes and research oxygen electrocatalytic properties.In this work,Fe-Co dual-single atom one-dimensional（1D）carbon nanotubes with synergistic effects were synthesized by coating metal templates layer by layer.The results shows that Fe-Co dual-single atom 1D carbon nanotubes have ORR and OER dual-functional activities and the hollow structure can expose the active site.1D tubular structures have electron transport capacity,The double metal active centers all showed single atom structure.the metal load reached 1.54 wt%.The half-wave potential(E_1/2)is 0.83 V,and the OER overpotential is 600 m V when the limiting current density（J）is 10 m A cm^-2,the potential difference（?E）is 1 V.（2）Preparation of ZnO nanoclusters by one-step carbonization and research oxygen electrocatalytic properties.In order to further solve the problem that Fe,Co and other transition metals are easy to generate high-valence oxide ions in ORR,which affects the battery life,and 1D structures are easy to stack and aggregate.The metal template structure is prepared into three-dimensional（3D）spherical structure,and the metal center uses metal Zn with full electron orbit(3d¹⁰4s²),which is more stable in the ORR.Due to the volatilization of Zn under 900℃,the metal template is removed and form a hollow structure by carbonization.In the high temperature process,a large number of multistage pore structures mainly composed of micropores are generated on the support with a surface ratio of 1183.84 m²g^-1,which is conducive to gas,liquid and electrons transmission,the metal load of the structure is 9.91 wt%.Electrochemical tests were conducted on the 3D hollow carbon spheres encapsulated by ZnO clusters,whose E_1/2=0.89 V,J=6.0 m A cm^-2.（3）Preparation of 3D biomimetic structure of Zn single atom with N defects and research oxygen electrocatalytic performance.Further regulation of the active core microenvironment and design of the support can improve the catalytic performance of the catalyst.Therefore,in this chapter,inspired by the special"branch-leaf"system of Oxalis herrerae,this chapter adopted the bionic strategy a flower-shaped 3D biomimetic carbon nanotubes structure of atomically dispersed Zn with N-defects（Zn-N-C-2）,which was synthesized by secondary carbonization.The N-defects structure of Zn-N₃-D catalyst was proved by density functional theory（DFT）and synchrotron radiation（XAS）.The catalyst showed excellent ORR and OER bifunctional activity,E_1/2=0.85 V,and OER overpotential is 450 m V at J=10 m A cm^-2.The drainage ZAB assembled as an air cathode catalyst shows a long-term charge-discharge performance of more than 200 h.