Preparatin And Performance Study Of Pd-based Trimetallic Cayhode Catelyst For Oxygen Reduction Reaction

Facing the global energy crisis and environmental pollution,it is extremely urgent to develop and utilize hydrogen energy resources to develop high-efficiency and pollution-free fuel cell technology.With the high cost and relatively low durability of the catalysts,the commercialization of PEMFCs remains a challenge.In recent years,non-platinum metal catalysts,especially Pd catalysts,have received an enormous amount of attention due to their huge potential in the oxygen reduction reaction.Pd and Pt have similar outer electronic structures,physicochemical properties,while Pd has advantages in reserves and prices compared to Pt.Studying and developing Pd-based catalysts with huge catalytic activity and stability is useful in theory and application1.The PdCoNi/C nanoparticles doped with different transition metal ratios(Co,Ni)were prepared by simple impregnation reduction method.Then the nanoparticles annealed in a hydrogen-argon mixed gas to improve the alloying degree.The physical characterization proves that the Pd2CoNi/C catalyst has higher crystallinity,smaller particle size and distribution on the support.The addition of transition elements significantly changes the coordination of the the active site.The electrochemical results show that there are many catalytic active sites on the surface of Pd2CoNi/C catalyst,the half-wave potential reaches 0.845 V,which is close to 0.865 V of Pt/C catalyst,and the 4-electron reaction mechanism is carried out during the reaction.2.The phase state of nanoparticles plays a pivotal role in regulating the electronic structure of Pd to enhance the catalytic performance and durability for the oxygen reduction reaction(ORR).To elucidate the correlation of the electronic structure with activity,a series of body-centered cubic(bcc)PdCu/C,PdCuFe/C and PdCuCo/C intermetallic compounds were fabricated by using an impregnation reduction method followed by annealing.The results of rotating disk electrode(RDE)shows that the structurally ordered PdCuFe/C nanoparticles exhibit a much larger increase in mass activity(0.08 A mg Pd-1),which is about 2.1 and 5 times higher than ordered PdCuCo/C and PdCu/C.More importantly,the maximum power density of the ordered PdCuFe/C was 267 mW cm-2 in proton exchange membrane fuel cells(PEMFCs).The X-ray photoelectron spectroscopy(XPS)results revealed that that the incorporation of Fe into PdCu/C can efficiently regulate the electronic structure of Pd in optimizing the oxygen binding energy for ORR.3.The porous structure PdCu@Pt/C catalyst was prepared by impregnation reduction method and spontaneous displacement reaction.TEM show the morphology of the catalysts reaction at different reaction times.Indicating the catalyst with hollow was formed when the reaction time was 6-hours.The electrochemical test showed that compared with the hollow structure,PdCu@Pt/C and multi-branched PdCu@Pt/C catalyst,the porous structure PdCu@Pt/C can significantly improve the catalytic oxygen reduction efficiency due to the large specific surface area and the high-index crystal plane exposed on the catalyst skeleton.Among them,the halfwave potential of PdCu@Pt/C reaches 0.921 V,a significant positive shift in E1/2 of?22 mV from that of Pt/C.The mass activity of PdCu@Pt/C-6 h is 8.5 times that of Pt/C.It has excellent oxygen reduction catalytic efficiency.The stability test shows that the Pt layer atoms on the surface of the porous structure effectively reduce the dissolution of Cu atoms in the catalyst.After 10,000 cycles of cyclic voltammetry,the half-wave potential degradation is only 8 mV,indicating excellent catalytic ORR stability...