Preparation Of Rare Earth-3d Transition Metal Composite Catalyst And Its Oxygen Electrocatalysis

The issue of energy and environment is still an urgent priority and difficult problem in our country.It is important to develop new energy storage and conversion devices for renewable green and new energy system.Electrocatalytic oxygen reactions play a considerable role among numerous energy conversion and storage devices,such as fuel cells,water-splitting devices,metal-air batteries,and so on.However,due to the limitation in reaction kinetics,the electrocatalytic oxygen reaction process needs to provide huge overpotentials above the theoretical potential to accelerate the electrode reaction,which undoubtedly causes additional energy loss.Traditional noble metal catalysts,such as Pt,Ru,and Ir and their oxide catalysts,are expensive due to their scarcity and suboptimal stability during catalysis,which hindering the large-scale application of electrocatalytic oxygen reactions and energy conversion and storage devices.3d transition metal-based catalysts have been regarded as a priority to replace noble metal-based catalysts due to their high natural abundance,low price,and environmental friendliness.However,they are difficult to apply in practical energy conversion devices due to their low intrinsic activities.Considering of the electronic structures,the modification of 3d transition metal-based catalysts with foreign elements may be a reliable strategy to regulate their catalytic performance.Owing to the unique chemical and electronic properties of 4f subshell electrons,rare-earth metals have potential applications in tuning the electronic structure and catalytic performance of various transition metal-based materials.Rare earth elements can be used as additives or promoters,which could tune the electronic structure of 3d transition metals and optimize the adsorption energy between the active sites and reaction intermediates and effectively improve their electrocatalytic performance.In this paper,we designed and synthisized a series of rare earth-3d transition metal-based catalysts with different compositions,sizes,and binding forms with transition metal-based materials.Besides,we also explore their catalytic behaviors and catalytic mechanisms in electrocatalytic oxygen reactions in detail.Through a careful exploration of the composition structure,electrochemical properties,active components,and catalytic mechanism of rare-earth-3d transition metal-based composites,the co-catalytic behaviors and mechanisms of rare-earth metal-based materials are deeply studied,which demonstrate the promising research prospects of rare-earth metals in energy storage and conversion applications and provide some new ideas for subsequent studies of rare-earth based materials.The main research works in this thesis are as follows:1.An efficient strategy to construct rare-earth oxides-3d transition metal phosphides heterostructure was designed and developed here.We employed a one-step hydrothermal and selective phosphidation approach to in situ anchor ceria particles onto the surface of rough Co P nanosheets to obtain a Co P/Ce O₂ heterostructure catalyst with abundant heterointerface.The modification of Ce O₂ particles on the surface of Co P nanosheets can provide abundant heterogeneous interfaces of Co P-Ce O₂,thus changing the electronic state of Co P,optimizing the ratio of Co²⁺/Co³⁺,and generating more oxygen vacancies,which will improve their OER catalytic activities.Benefiting from the synergistic effect between Co P and Ce O₂,the as prepared Co P/Ce O₂ catalyst exhibited much superior OER electrocatalytic activity with lower overpotential,larger current density,smaller Tafel slope,and excellent electrochemical stability than those of the Co P catalysts and the commercial Ru O₂ catalyst.It is worth mentioning that the Co P/Ce O₂ catalyst delivers a low overpotential of only 224 m V at 10 m A cm^-2 in the OER,which far exceeds that of the commercial Ru O₂ catalyst.When applying as an air cathode for Zn-air batteries,the Co P/Ce O₂+Pt/C-based Zn-air batteries exhibit an ultralong life cycle life,which is far superior to that of commercial Ru O₂+Pt/C hybrid catalysts.This study demonstrates the importance of rare earth-3d transition metal interface engineering and oxygen vacancies in the development of high-performance electrocatalysts.2.A simple and effective sol-gel strategy was developed to fabricate Gd₂O₃-Co/N-doped graphene(Gd₂O₃-Co/NG)hybrid materials.Besides,the charge transfer behavior and ORR reaction mechanism at the interface of rare-earth and transition metal materials were systematically explored.The incorporation of Gd₂O₃ into metallic Co could make the charge redistribution at the engineered interface of Gd₂O₃/Co,creating more oxygen vacancies and optimizing surface electronic structure of catalyst,resulting in high ORR catalytic activity and stability for Gd₂O₃-Co/NG.In addition,DFT theoretical calculations demonstrate that the binding of Gd₂O₃-Co can effectively optimize the adsorption of intermediate oxygen species on the surface of catalysts.Benefiting from the synergistic effect between Gd₂O₃ and metallic Co,Gd₂O₃-Co/NG catalyst exhibits excellent ORR activity with a half wave potential of 0.82 V,which is comparable to that of commercial Pt/C catalysts.As an air–cathode in Zn–air batteries,the Gd₂O₃-Co/NG exhibits a large power density(114.3 m W cm^-2),a high energy density(892.7 Wh kg _Zn^-1),and an excellent cyclability(over 160 cycles at 10 m A cm^-2).This work explores the charge transfer behavior at the interface of rare earth-3d transition metal materials.The catalytic mechanism of catalysts was also explored.We believe that this work will make a significant impact in the development of rare-earth doped materials for the energy storage and conversion.3.An efficient and novel Gd doping strategy was developed to improve the OER performance of Ni Fe-LDH.And the effects of Gd element incorporation on LDH composition,structure and catalytic behavior were systematically explored.We first designed and synthesized carbon cloth supported Gd doped Ni Fe-LDH nanosheet arrays by a facile hydrothermal method(Gd-Ni Fe-LDH@CC).It was found that the incorporation of Gd into Ni Fe-LDH could effectively adjust the electronic structure of the host LDH material,promote the charge transfer efficiency of the catalyst and increase the oxygen vacancies of the material,which is beneficial for the OER process.In addition,DFT theoretical calculations demonstrate that the doping of Gd could increase the reaction activity of Ni sites in Ni Fe-LDH and optimize the adsorption energy of intermediate oxygen species on the surface of catalyst.Compared with Gd-free Ni Fe-LDH@CC,Gd-Ni Fe-LDH@CC exhibited remarkable OER activity with a low overpotential of 210 m V at 10 m A cm^-2,long-term stability,and selectivity with nearly 100%Faraday efficiency.As an OER electrode for water-splitting devices,Gd-Ni Fe-LDH@CC exhibited an extremely low cell voltage of only 1.46 V and could well maintained even after continuous electrolysis for 22 h.This work explores the effect of doping rare-earth atoms into transition metal host materials on the electronic structure and catalytic behavior of catalysts in detail.