Rational Design Of Transition Metal/Carbon Hybrid Materials And Application Of Reversible Oxygen Catalysis

With the increasing demand for energy and the rapid consumption of fossil fuels,the development and utilization of clean energy has become one of the important ways to achieve sustainable development.Rechargeable Zinc-air batteries（ZABs）are considered to be one of the most promising energy conversion devices due to their high energy density,high safety and low cost.The bifunctional catalytic activities of oxygen reduction（ORR）and oxygen evolution（OER）reactions are important for the development of rechargeable zinc-air batteries.The different reaction mechanisms and kinetic processes between ORR and OER make it a major challenge to design suitable non-noble metal catalytic materials to catalyze both reactions at the same time and to develop high-performance rechargeable ZABs.Transition metals are abundant and diverse on Earth,and have excellent electrical conductivity,and the outer electrons are easy to change,which makes the valence states of elements diverse.In recent years,in the direction of ORR and OER electrocatalysis,researchers have made an extensive exploration of many transition metal-based materials.Through reasonable precursor design and high-temperature heat treatment strategy,a transition metal organic framework（MOF）precursor system can be prepared into electrocatalytic materials with excellent performance.This paper highlights the application of asymmetric transition metal active sites constructed in advanced and stable carbon-based support in reversible oxygen catalysis,characterizes the structure and morphology of hybrid materials,and explains the structure and composition of the catalyst and the catalytic mechanism and activity law through theoretical calculation.The main research contents and results are as follows:1.Based on a"chemical etching/in situ capture"synthesis strategy,a unique bivalve carbon-based nanocapsules with integrated size-asymmetric Co monatomic(Co _SA)and metallic Co nanoparticles(Co _NP)components have been prepared.The well-formed catalysts showed significant bi-functional electrocatalytic activity in alkaline electrolytes,with ORR half wave potential of 0.886 V and OER over potential of 341 m V at current density of 10 m A/cm².In addition,the double-shell carbon nanobox catalyst is an efficient oxygen electrode in the assembled rechargeable ZABs,with a peak power density of 239m W/cm² and a specific capacity of 770 m Ah/g _Zn.The charge-discharge cycle stability is significantly better than that of the Pt/C-Ru O₂ electrocatalysts.The theoretical calculation shows that the strong interaction between the Co _SA site with asymmetric size and the Co _NPphase can effectively optimize the adsorption and desorption energy barrier of the reaction intermediates on the designed catalyst surface,so as to achieve the synergistic enhancement of the electrocatalytic activities of ORR and OER.2.Based on the"conformal coating and coordination capture"pyrolysis strategy,a unique macroporous nanoframe structure was constructed,in which Fe-Co/Mo₂C Mott-Schottky heterojunction with asymmetric components was coupled to the nitrogen-doped carbon matrix.Due to the synergism and structure of multiple active centers,OER has a low overpotential of 277 m V at 10 m A/cm² and ORR has a high half-wave potential of0.872 V in alkaline electrolyte.The voltage difference between the two catalysts,ΔE(ΔE=E_j=10-E_1/2),is also very small,only 0.635 V.In addition,as an economical and efficient oxygen electrode,the synthesized catalyst showed excellent electrochemical performance in rechargeable ZABs,with a peak power density of 218 m W/cm²,a specific capacity of694 m Ah/g _Zn,and a stable charge-discharge cycle of more than 240 hours.Theoretical calculations have confirmed that the internal electric field between the asymmetric Fe-Co alloy and Mo₂C can induce favorable charge transport and redistribution at the heterogeneous interface,which is helpful to optimize the d-band center of the nano complex and reduce the reaction energy barrier during the catalytic process.Figure[53]Table[8]Reference[150]...