Preparation Of Doped Porous Carbon-based Catalyst And Its Application In Li-O₂ Battery

Energy shortage and environmental pollution caused by the burning of fossil fuels are recognized as the most serious challenges to the world.Developing environmental-friendly and sustainable clean energy technologies has become the most important and urgent research topic all over the world in recent years.In this background,Li-oxygenbattery has attracted huge attention owing to its ultrahigh theoretical energy density.Great efforts have been paid to this novel energy technology,and great achievements have been obtained.However,it still remains a lot of scientific and technical issues need to be addressed.Among them,exploring highly efficient and stable cathode materials has become one of the most important topics inbattery field.Doped carbon materials are demonstrated as a promising cathode forbattery due to its low cost,good electron conductivity,excellent oxygen reduction performance and easy modulation of structures.Although carbon materials are easy to react with electrolyte and discharge products at high potential,lightweight carbon materials can achieve high specific capacities ofbatteries,which is the main reason of continuous researching carbon materials inbatteries.In order to address the issues of corrosion and the insufficient oxygen evolution reaction activity,precious metals of high catalytic activities are often integrated with the carbon materials to improve the performance ofbatteries.Besides carbon materials,transition metal oxides are often used forbatteries,which possess the advantages of low cost,excellent catalytic activities and efficiently avoiding the corrosion problems of carbon,thus greatly enhancing the battery performance.In this thesis,biomass and MOF were tried as the precursors to prepare highly catalytic active cathode materials forbatteries.The main contents are as follows:?1?With MOF derived carbon material?MDC?of Fe-N-C structure as the substrate,Ru and Mo O3 nanoparticles were highly dispersed on it by impregnation method associated with H2reduction and the resulted composite was used as electrode forbatteries.The results manifest that the MDC possesses abundant regular pores,which is beneficial for the high dispersion of Ru and Mo O3 nanoparticles.Ru nanoparticles can efficiently modulate the adsorption of oxygen species on the surface of catalysts and improve the"excessive"growth of discharge products,which is favorable for increasing the discharge capacity,lowering the overvoltage and enhancing the cycle life of the batteries.Loading Mo O3 nanoparticles doesn't show much effect on improving the discharge specific capacity,but they can adjust the surface electronic structure of the catalysts,thus effectively enhancing the stability of the batteries.The battery exhibits the best performance with Ru-Mo,delivering a specific capacity of 5343 m Ah g^–1 and a charge voltage platform of 4.0 V at 100 m A g^–1.With the specific capacity limited to 600 m Ah g^–1,the Ru-Mocathode can operate stably for 160 cycles.?2?With cheap biomass containing abundant N and S,one kind of porous doped carbon material with high specific surface area was prepared by using the principle of foaming with Fe³⁺.The results showed that the GPDC-2 cathode achieved an extremely high specific capacity of 13634 m Ah g^–1 at the current density of 100 m A g^–1 and the discharge medium voltage platform was 2.75 V.This is mainly attributed to the high specific surface area of GPDC-2(1561.0 m² g^–1),which can provide numerous active sites and three-phase reaction interface.Meanwhile,the organized porous structure can facilitate the diffusion of O2 and Li⁺,the infiltration of electrolyte and the storage and decomposition of discharge products.Unfortunately,GPDC-2 shows poor cycling stability,running only 28 cycles at 100 m A g^–1with the limited specific capacity of 600 m Ah g^–1 from 2.0-4.5 V.?3?The main reason of poor cycling performance of GPDC-2 is the insufficient catalytic activity towards oxygen evolution reaction,leading to the high charge overpotential and incomplete decomposition of the discharge products.In order to solve these problems,we tried loading different amounts of Ru O2 nanoparticles on the GPDC-2 substrate to improve the OER performance and using them forbatteries.Among them,the cathode with15%Rushowed the best performance.The discharge capacity was 10751 m Ah g^–1at 100 m A g^–1,and the median voltage of discharge and charge was 2.7 and 3.9 V,respectively.With the limited capacity of 600 m Ah g^–1 and the limited voltage of 2.0-4.5 V,such cathode could operate 306 cycles.The results show that Ru O2 nanoparticles can effectively lower the charge overvoltage,decompose the discharge products,and enhance the cycle stability ofbattery.?4?A free-standingsheet array cathode was prepared by in situ synthesis of an array of sword-like Co-MOF sheets on a carbon cloth?CC?substrate,followed by impregnation with nickel nitrate solution and pyrolysis in air flow and used as a cathode forbatteries.The self-supporting electrode also efficiently avoid the adverse reactions between the binder and electrolyte or the discharge products.We suggest the high performance of our cathode can be ascribed to its well-defined 3D sheet array structure,which can facilitate the O2 diffusion and electrolyte impregnation,provide sufficient space for storage of the discharge products.Moreover,thanks to the synergistic effect betweenand Ni,thecathode exhibited better performance than either single-componentor Ni.Such cathode achieved a specific capacity of10645 m Ah g^–1 at 100 m A g^–1,which was much higher than that of(6773 m Ah g^–1)or Ni(9354 m Ah g^–1).The discharge and charge plateaus withcathode were 2.7 and 4.0 V,respectively.In addition,thehybrid cathode also exhibited high stability of 225 cycles without apparent degradation of both discharge and charge voltages.