Study On The Electrocatalytic Performances Of Pd-based Nanomaterials By Engineering The Electronic Structures

Energy electrocatalysis,taking alcohol oxidation,oxygen reduction（ORR）and oxygen evolution reduction（OER）as representative,is the core technology and key bottleneck of the next generation clean and efficient energy systems such as fuel cells and metal air batteries.These reactions involve multi-step proton-coupled electron transfer process and have high overpotentials,limiting the energy efficiency.At present,a great deal of research work focused on the development of catalysts.Pd,as one of Pt group metals,has attracted much attention due to its relatively abundant sources,low cost and high stability,but its electrocatalytic activity still needs to be improved compared with Pt.As we all known,the intrinsic activity of catalysts is closely related to their electronic structure.Therefore,the electrocatalytic performance of Pd-based catalysts can be improved by regulating the electronic structure and optimizing the surface composition and structure.In this paper,Pd-based catalyst is taken as research object.On the basis of conventional preparation methods,a more simple and controllable preparation method of Pd-based catalytic materials is explored.The surface structure,surface composition and electronic structure of Pd-based catalysts are regulated by introducing defects indirectly or directly,forming heterostructures or alloys,doping and forming lattice dislocations,and the electrocatalytic performance has significantly improvement.The main research contents are as follows:1.Metal PdCo precursors were synthesized by a simple and convenient wet chemical reduction method.After in situ annealing of PdCo precursors,Co in the precursor metal PdCo was oxidized to CoOx,and part of Pd was oxidized to PdO,resulting in Pd-PdO-CoO_x.According to the XRD,XPS and TEM characterizations,the obtained metal PdCo has a tightly connected heterostructure.After in-situ oxidation treatment,the morphology,composition and electronic structure of the active components takes place obvious changes compared with its precursor PdCo（1:4）.After in-situ annealing,there is a strong interaction between Pd and PdO-CoO_x,which can stabilize and change the electronic structure of Pd nanoparticles through the interface and/or electron transfer between Pd and PdO-CoO_x.This electron transfer can reduce the d-band center of Pd and the adsorption energy of toxic intermediates on Pd surface,which will help to remove intermediates and improve the electrocatalytic performance.2.Introducing heterojunction strategy is an important method to control the electronic structure of materials.PdCo-300 nanomaterials（PdO embedded in Co₃O₄ nanoparticles）were prepared by a simple and effective method.The results show that PdCo-300 nanomaterials have abundant heterojunction interface and oxygen vacancies,which can effectively change the electronic structure of nano-catalytic materials and enhance ORR/OER bifunctional electrocatalytic performance.In addition,the preparation method is simple and can be easily extended to other multi-functional materials,such as solar cells,fuel cells and other heterogeneous catalysts.3.Heteroatoms doping is also an important strategy to control the electronic structure of materials.PdCu alloy with multiple branches is prepared by solvothermal method.A series of experiments show that the morphology of PdCu alloy can be effectively adjusted by introducing Cu²⁺.Compared with commercial Pd/C and pure Pd,the prepared PdCu alloy catalyst exhibits higher electrocatalytic activity and stability for EGOR due to the three-dimensional superstructure of multi-branch,the change of electronic state of Pd and the synergistic effect between Pd and Cu.It opens up a new way for the controllable synthesis of bimetallic alloys and effective electronic structure control,and provides an ideal choice for EGOR catalysts with high activity and durability.4.The surface structure of catalytic materials is closely related to their catalytic performance.PdRuCu catalyst was synthesized by one pot solvothermal method.The TEM characterization shows that a large number of lattice mismatches existes in the PdRuCu catalyst.The lattice dislocation changes the charge distribution on the catalyst surface and electronic structure.Compared with commercial Pd/C,the prepared PdRuCu catalyst exhibits higher electrocatalytic EGOR activity and excellent stability due to its special surface structure,the change of palladium electronic state and the synergistic effect between Pd and Cu and Ru.This provides a new possibility to improve the electrocatalytic performance of electrocatalytic materials by dislocation engineering.It also provides a new choice for EGOR catalysts with high activity and durability.