The Construction,preparation And Properties Of Rare Earth-based Oxygen Reduction Catalytic Materials

Oxygen reduction reaction is a key process at the air side of fuel cells and metal-air batteries devices,involving O₂ adsorption,O-O bond activated dissociation,and O species removal on the electrode surface.Due to the inherently sluggish reaction process,oxygen reduction reaction has become the main limiting factor of conversion efficiency in these energy devices,so high-efficiency oxygen reduction catalysts are indispensable in these devices.So far,the noble metal Pt is considered as the most efficient catalyst for oxygen reduction,however,the cost and stability issues of Pt have seriously hindered its large-scale commercial application.Therefore,oxygen reduction catalysts with low cost,high efficiency and good stability have been extensively studied.Rare earth metals have received extensive attention due to their special physical and chemical properties derived from their special 4f shell electronic configuration.They have strong coordination ability with reactant molecular orbitals.Rare earth oxides have the characteristics of oxyphilic and variable valence states,oxygen vacancies are relatively easy to form.They are often used as promoters to participate in redox reactions,which can not only protect the high catalytic active site of the main catalyst,but also transfer the O species to the active site during the oxygen reduction reaction.These characteristics enable rare earth to participate in the electrocatalytic reaction of oxygen as a main or auxiliary catalyst.Based on the defects of current catalysts and the advantages of rare earth oxides,this dissertation focuses on the controllable construction of rare earth oxides and their composite materials,and their electrochemical oxygen reduction performance are explored,air batteries are used to evaluate its practical application performance.The main research contents and results of this dissertation are as follows:1.Rare earth oxide ReO_x/NC as oxygen reduction catalyst and its Zn-air battery performance.A series of amorphous uniformly dispersed ReO_x/C samples were prepared by a simple method of solvothermal.By studying the different mass ratios of ReO_x and C,the optimal ORR activity is obtained.After calcination in a mixed atmosphere of NH₃/Ar,due to the good interaction between ReO_x and the N-doped C support,the oxygen reduction performance of ReO_x/NC is enhanced,which is better than that of ReO_x/C and N-doped C.Among them,Pr₆O₁₁/NC shows the best oxygen reduction activity.The oxygen vacancies of Pr₆O₁₁/NC after calcination are enhanced,which facilitates the adsorption and transfer of O species.At the same time,the stability of Pr₆O₁₁/NC is also enhanced.The Zn-air battery assembled with Pr₆O₁₁/NC as the cathode catalyst shows good electrochemical performance.We systematically studied the ORR performance of ReO_x/C,even the practical application in Zn-air battery,so we believe that it can lay a good foundation for further exploration of rare earth based ORR catalyst with higher ORR performance.The oxygen reduction performance of rare earth oxide catalysts is systematically studied,and the practical application prospects are evaluated by the assembled zinc-air battery.This provides a good foundation for future better catalyst designs.2.Eu₂O₃-Cu/NC composite catalyst as a high-performance oxygen reduction catalyst and its Zn-air battery performance research.Novel Eu₂O₃ and Cu-supported N-doped carbon electrocatalyst Eu₂O₃-Cu/NC was successfully prepared by simple solvothermal and high temperature calcination methods,its oxygen reduction performance in alkaline environment and the performance of assembled zinc-air battery are investigated.The onset potential,half-wave potential,and limiting current density of Eu₂O₃-Cu/NC are 0.923,0.791 V and 5.86 m A·cm^-2,respectively,which are much higher than that of Eu₂O₃/NC and Cu/NC,and even larger than the limiting current density of Pt/C catalyst(5.54 m A·cm^-2),showing excellent oxygen reduction activity.The introduction of Eu₂O₃ brings huge oxygen vacancies,which is very helpful for the adsorption and transfer of O species,the total amount of N doping and the content of pyridine N in the high-temperature calcination stage are increased.At the same time,there is a strong interaction between Eu₂O₃ and Cu.The grain boundaries of the two species are in close contact with each other,which realizes the effective migration of O species between Eu₂O₃ and Cu species during the oxygen reduction process,so that the onset potential,half-wave potential and limiting current density have been improved.In addition,due to the interaction of active sites,the stability of Eu₂O₃-Cu/NC are also enhanced.The Zn-air battery assembled with Eu₂O₃-Cu/NC catalyst shows good electrochemical performance.Its peak power density(83 m W·cm^-2)is higher than that of Pt/C(71 m W·cm^-2),proving the prospect of practical application.Therefore,this provides an example for the application of novel rare earth and transition metal composite materials in the field of electrocatalysis.It also provides a feasible way for the design of high-performance and low-cost oxygen reduction electrocatalysts by adjusting the types of non-precious metals or precious metals,and then compositing appropriate rare earth oxides.3.Rare earth insitu-doped ZIF-67 derived Sm₂O₃-Co/NEC300J as a high-performance oxygen reduction catalyst and its Al-air battery performance research.Sm-ZIF-67/EC300J is prepared by in-situ Sm-doped ZIF-67 and the simultaneous carbon coupling process,then Sm₂O₃-Co/NEC300J with carbon encapsulated Sm₂O₃-Co nanoparticles is successfully obtained by subsequent high-temperature carbonization.The onset potential,half-wave potential and limiting current density of Sm₂O₃-Co/NEC300J are 0.924 V,0.811 V and 5.17 m A·cm^-2,respectively,and Sm₂O₃-Co/NEC300J exhibits excellent stability,equivalent to Pt/C.The Al-air battery assembled with Sm₂O₃-Co/NEC300J as the cathode catalyst exhibits a discharge voltage of approximately 1.225 V,a discharge specific capacity of 1588 m Ah·g_Al^-1,and a peak power density of 62 m W·cm^-2,it also has good stability during deep discharge,these performance indicators are better than Pt/C catalysts,so it has good application prospects in the energy field.The introduction of Sm₂O₃significantly improves the electrocatalytic performance of oxygen reduction reaction.Due to the synergistic effect of Sm₂O₃ and Co,the onset potential,half-wave potential and limiting current density are all improved.The introduction of Ketjen black EC300J brings a limited pyrolysis environment to promote the formation of a carbon encapsulated structure,generating a large number of oxygen reduction reaction active sites.The transfer of electrons from Sm₂O₃ to Co species is proved by XPS,so the existence of interaction is confirmed.This kind of interaction enables the Sm₂O₃-Co/NEC300J catalyst to exhibit more excellent oxygen reduction performance even when the activity of the intrinsic oxygen reduction active sites decreases.This result once again reveals that the interaction has a huge impact on the oxygen reduction performance.Even after a small amount of rare earth is introduced,it still has a huge impact on the performance.This interaction between rare earths and transition metals,which are generated from the atomic level,provides a solution for further design of high-performance oxygen reduction catalyst.4.Polyaniline coated Tb-Fe bimetallic MOF derived Tb₄O₇-Fe/NC as a high-performance oxygen reduction catalyst and its Zn-air battery performance research.Tb₄O₇-Fe/NC electrocatalyst was successfully prepared by pyrolysising polyaniline coated Tb-Fe-BTC,with the structure of Tb₄O₇,Fe₃N and Fe₄N composite supported N-doped carbon.The initial potential,half-wave potential and limiting current density are 0.989 V,0.840 V,5.18 m A·cm^-2,respectively,which are equivalent to Pt/C catalyst,showing excellent oxygen reduction activity.Tb₄O₇-Fe/NC catalyst has a relatively good number of active sites,as well as high active sites of Fe₃N and Fe₄N.Due to the interaction between Tb₄O₇ and Fe species,the oxygen reduction activity and stability of Tb₄O₇-Fe/NC is better than Tb₄O₇/NC and Fe/NC catalyst.The Zn-air battery assembled with catalyst as the air electrode catalyst shows good electrochemical performance.Compared to the Zn-air battery constructed by Pt/C,the peak power density of Tb₄O₇-Fe/NC based Zn-air battery(111 m W·cm^-2)is much higher.During the entire discharge process,the voltage plateau is also relatively high.Besides,Tb₄O₇-Fe/NC based Zn-air battery presents excellent cycle stability and rate capability,demonstrating a prospect of practical application.