Design And Synthesis Of Bimetallic Sulfide Electrocatalytic Materials And Their Application In Zinc-air Batterie

Human society cannot develop without relying on energy resources,yet excessive energy consumption has led to a series of environmental problems,which have sounded the alarm for mankind and sustainability has attracted widespread attention.The need for green and sustainable energy has led to the development of chemical batteries and energy conversion technologies.Zinc air battery（ZAB）is a promising electrochemical energy storage device that has received a lot of attention from researchers due to its lo w cost,higher energy density,safety and efficiency.Precious metals are commonly used as catalytic materials for air electrodes,with Pt and its alloys being the common electrocatalysts for the oxygen reduction reaction（ORR）and Ru O₂ or Ir O₂ for the oxygen evolution reaction（OER）.However,the high cost,low reserves and poor durability of precious metals have seriously hindered their large-scale engineering applications.In addition,the slow ORR and OER kinetics and single catalytic effect of noble metal materials result in high overpotential and poor bifunctional catalytic performance of the air cathode,which seriously affects the performance of ZAB.Therefore,there is an urgent need to develop efficient,cheap and clean bifunctional electrocatalysts capable of d riving both ORR and OER reactions.Transition metals are popular catalytic materials that can replace precious metals.In addition to their large reserves,transition metal elements have more unfilled d orbitals in their outer layers and have a tunable electronic structure,which facilitates the formation of complexes with reactants and enhances electrocatalytic activity.However,transition metal compounds generally have the disadvantage of low electrical conductivity.If the transition metal compounds are compounded with conductive carbon materials to reali ze the complementary advantages of the two types of materials,the electrocatalytic activity and stability of the ORR and OER reactions can be further enhanced.In this thesis,a series of composites with high catalytic activity have been prepared based on bimetallic sulfide electrocatalytic materials by means of phase structure conversion and heteroatomic substitution,which can be controlled to adjust the electronic structure of the active site.They were applied to zinc air batteries as air-cathode catalysts.The main studies are as follows:（1）Single-phase metal sulfide CoFe S₂/NC and biphasic sulfide heterojunction Co S-Fe S/NC catalysts,both of which have a typical core-shell structure,were successfully synthesized by a simple co-precipitation and calcination process.Compared to Co S-Fe S/NC,the single-phase bimetallic sulfide CoFe S₂/NC exhibited excellent electrocatalytic performance.In particular,for ORR,CoFe S ₂/NC has an onset potential and half-wave potential of 0.84 and 0.76 V,respectively.For OER,CoFe S₂/NC has overpotentials of 340 and 370 m V at 10 and 50 m A cm^-2,respectively.thanks to the excellent bifunctional catalytic performance,when the CoFe S ₂/NC catalyst is used as the air cathode in a rechargeable zinc air battery,CoFe S₂/NC has significant cycling stability compared to noble metal catalysts,and its high electron density structure,fast charge transfer capability and synergistic interaction with NC result in excellent elec trocatalytic performance.The results of this chapter show that controlled phase structure conversion of metal sulfides can efficiently promote their electrocatalytic activity in zinc air batteries.（2）A CuCo₂O_4-xS_x/NCNTs catalyst was prepared as an efficient catalyst for OER and ORR using trace S atomic-level substitution.The XRD,XPS,AC-TEM and XAFS results illustrate the change in coordination form with the coexistence of Co-O and Co-S as S enters CuCo₂O₄.DFT calculations showed that the introduction of S int o CuCo₂O₄lattice could modulate the three-dimensional electronic structure by optimizing the electron distribution,and compared with CuCo₂O₄/NCNTs and CuCo₂S₄/NCNTs,the bifunctional activity of the OER and ORR of the CuCo₂O_4-xS_x/NCNTs catalyst was better than that of CuCo₂O₄/NCNTs and CuCo₂S₄/NCNTs,mainly reflected in an overpotential of 340 m V at 10 m A cm^-2 and an ORR half-wave potential of 0.75 V.When used as an air cathode in zinc air batteries,the open-circuit potential of the battery was 1.43 V,and most of the performance was maintained after 300 h of cyclic stability testing.Most of the performance was maintained after 300 h of cycling.The present work demonstrates the importance of S doping in bifunctional oxides to improve the intrinsic activity of electrocatalysts and provides a new strategy for the rational design of low-cost and efficient multifunctional catalysts for rechargeable zinc air batteries energy storage device applications.