Structure And Electrocatalytic Performance Of Palladium-Based(Fe、Co、Zn)Nanomaterials

It is theoretically and practically important to explore the low cost and high active catalysts.This thesis focuses on the research of Pd-based nanocatalysts.The structure of Pd-M alloy catalysts could be precisely controlled by regulating the type of transition metal,ratio of Pd to M,annealing temperature and the structural transformation from disordered to ordered structure.The structure change may cause the shift of d-band center and the change of electronic structure of Pd,resulting in the enhancement of catalytic performance.The ORR/HOR performance could be further improved by Pt/Au decoration.The structure-activity relationship between the electronic structure of Pd and catalytic performance can further guide the optimum design of the catalyst.The research contents are as follows:（1）The structure-activity relationships between the structure of Pd and ORR catalytic performance are constructed by regulating the annealing temperature and ratio of Pd to Co/Zn.The higher temperature can increase the alloying degree and particle size,resulting in the existence of a volcanic-relationship curve between the ORR activity and the temperature.At the same temperature,there is a volcanic-relationship curve between the ORR activity and the atomic proportion,and then Pd₈CoZn/C catalyst exhibit the best catalytic performance.The ORR activity and stability can be further enhanced by forming Pd₈CoZn@Pt/C core-shell structure catalysts.（2）Fe₂O₃ shell could be spontaneous formed on Pd₂FeCo/C nanoparticle and could effectively prevent the particles aggregation during forming higher alloy degree.Hence,the alloying degree of PdCo/C,PdFe/C and Pd₂FeCo/C catalyst are diverse.There is a volcanic-relationship curve between the ORR catalytic performance and the alloying degree,and then Pd₂FeCo/C catalyst exhibits the highest mass activity and specific activity.The ORR activity and stability can be further enhanced by forming Pd₂FeCo@Pt/C core-shell structure catalysts.Pd₂FeCo@Pt/C catalysts exhibit high power density and stability when used as the ORR catalyst for Zn-air battery.（3）By regulating the annealing temperature and ratio of Pd to Fe,the disordered PdFe（D-PdFe/C）can be transformed to ordered intermetallic PdFe phase（O-PdFe/C）.The O-PdFe/C could precisely control the lattice parameter and electronic structure of Pd and then enhance the ORR catalytic activity and stability.The ORR performance could be further enhanced by Pt decoration to form O-PdFe@Pt/C catalysts.When used as the ORR catalyst for Zn-air battery,O-PdFe@Pt/C catalysts exhibit high power density and cycling stability.Furthermore,different amounts of Au modified O-PdFe/C catalysts were synthesized by a spontaneous substitution method.The stability increased and the ORR catalytic activity decreased with the increase of Au quantity.（4）By regulating the annealing temperature and ratio of Pd to Zn,the disordered PdZn（D-PdZn/C）can be transformed to ordered intermetallic PdZn phase（O-PdZn/C）.Compared with D-PdZn/C,O-PdZn/C exhibited higher ORR activity and stability in 0.1 M KOH solution.The ORR activity and stability could be further enhanced by Au decoration.When used as the ORR catalyst for Zn-air battery,Au-O-PdFe catalysts exhibit high power density and discharge durability.（5）By regulating the annealing temperature,the disordered PdFe（D-PdFe/C）can be transformed to ordered intermetallic PdFe phase（O-PdFe/C）.Compared with D-PdFe/C,O-PdFe/C exhibited higher HOR activity and stability in 0.1 M KOH solution.Forming core-shell structure O-PdFe@Pt/C catalyst can attenuate the adsorption of hydrogen and enhance the HOR performance,which can be proved by the calculation from density functional theory（DFT）.