Synthesis And Oxygen Reduction Properties Of Mesoporous Metal Oxide Supported Metal Pd Nanocomposites

Seeking for the advanced cathode catalysts with high acticity,selectivity and stability has been focused on current research for the fuel cell and the choosing of suitable catalysts support is one of the most important factors in affecting the performance of the catalysts.The catalysts support can overcome the problems such as dissolution,sintering and aggregation occur during the application in fuel cell of metal catalysts,and hence improve the catalytic activity and electrochemical stability of the catalyst.In addition,the catalysts support with mesoporous structure can also facilitate the diffusion,adsorption and transport of O2 during the process of oxygen reduction reaction(ORR).In this paper,the thesis aims at finding high effective catalysts by preparing novel mesoporous catalysts support.Three mesoporous metal-metal oxides nanostructures have been prepared by simple method.The EDS,XRD and N2 nitrogen adsorption-desorption isotherms have been used to characterize the component and microstructure.Additionally,we have been studied the electrocatalytic oxygen reduction reaction performance of Pd-Mn2O3 and Pd/rGO/PMo12.The work was summarized as follows:(1)In the system of aqueous solution,lauryl sodium sulfate(SDS)as surfactants,mesoporous flower-liked Mn3(PO4)2 nanostructures were prepared by a micro-emulsion method.XRD analysis shows that the nanostructures were amorphous structure.Corresponding N2 adsorption-desorption isotherms exhibits that there exist pore in the nanostructures.XPS spectra reveals that the valence states of Mn is+2 and PO43-is the main form of phosphate radical.Additionally,the morphology was changed when changed the amount of SDS.Based on the unique morphology and pore structure,and high specific surface area,Mn3(PO4)2 nanostructures were suitable supports for loading metal nanoparticles.Therefore,Pd-Mn3(PO4)2 nanostructures were obtained by facile solvothermal method.The morphology and structure of Mn3(PO4)2 had no change after loaing Pd nanoparticles.These results demonstrate that Mn3(PO4)2 nanostructures can use as a kind of catalysts support.(2)The synthesis of mesoporous Mn2O3 nanostructures were performed by modifying a micro emulsion method between Mn(Ac)2 and Na3PO4 in alkaline media.Tetrabutyl ammonium hydroxide aqueous solution(10%)was employed to adjust the pH value of the reaction solution.The morphology and composition of products had a great difference by adding different amount of Na3PO4.The results demonstrate that Na3PO4 is a template reagent in this system.Then,the Pd/Mn2O3 nanocomposites with different Pd loading amount were achieved by simple solvothermal method.Moreover,compared with Mn2O3,Pd/graphene,10%Pd/Mn2O3,the composites of Pd/Mn2O3 demonstrated a good competitive ORR activity and a high selectivity.Besides high activity,Pd-Mn2P3 nanocomposites also exhibited respectable catalytic stability in alkaline electrolyte,which is superior to the commerce Pt/C catalysts.The enhanced catalytic activity is attributed to the feature of mesoporous Mn2P3 nanostructure and the synergic effect between the Pd nanoparticles and support.(3)Mesoporous rGO/PMo 12 nanostructures have been successfully synthesized via ultrasonic method in the system of aqueous solution.Hydrazine hydrate was employed as the reducing agent to reduce graphene(GO)and phosphomolybdic acid(PMol2)simultaneously.In the FT-IR spectrum of the rGO/PMo12,a blue shift of the diffraction peaks and a new diffraction peaks at 1500 cm-1 are observed as compared with the single PMo12,indicating the conjugated interaction between the PMo12 and graphene.N2 adsorption-desorption isotherms analysis reveals that the as-prepared materials with mesoporous structure and the pore size is approximately 3.7 nm.We integrated Pd(NO3)2 to prepare ternary mesoporous Pd/rGO/PMo12 nanostructures based on the above system.The nanocomposites show a higher electrocatalytic activity towards ORR in direct methanol fuel cells.Electrocatalytic measurements demonstrate that those obtained Pd/rGO/PMo 12 nanostructures exhibit a higher current density and methanol-tolerant property compared with Pd/rGO.These results,combined with the synergetic catalytic effects,make these Pd/rGO/PMo12 nanostructures as suitable candidates catalysts for direct methanol fuel cells.