Synthesis Of Palladium-based Multimetallic Fuel Cell Catalysts And Their Electrocatalytic Performance

Proton exchange membrane fuel cell（PEMFC）can efficiently convert chemical energy to electricity with high power density and zero emission conditions,which is considered to be one of the most important technologies to replace the existing non-regenerated energy resources.The Pt-based materials have been the most widely used cathode/anode catalysts for PEMFC.However,the application and development of PEMFC are extremely restricted by the high cost and low persistence of pure Pt catalysts.Pd is a precious metal in the group of Pt.It also has good catalytic performance for the electrocatalytic reaction of PEMFC,and its reserves in the earth are higher than that of Pt.Based on this,the PEMFC catalysts with high performance,low cost and high stability have been designed and synthesized by regulating the Pd-based nanomaterials from the morphology,structure and composition,and their electrocatalytic properties for oxygen reduction reaction（ORR）and alcohol oxidation have been investigated.The main research contents and results are as follows:1.A method was designed to deposit ultra-small Pt nanodots with a size of about 3nm on decahedral Pd nanocrystals to form decahedral Pd@Pt core-shell nanodots arrays（Pd@PtNAs）.Pd@PtNAs were synthesized by the reduction of Na₂PdCl₄ and H₂PtCl₆using L-ascorbic acid（AA）as reducing agent,cetylpyridine chloride（CPC）and potassium bromide（KBr）as the stabilizing and crystal-regulating agents.Such ultra-small Pt nanodots arrays structure significantly increase the specific surface area and activity of the catalyst,thus improving the utilization efficiency of Pt atoms in the electrocatalytic process.Pd@PtNAs were prepared with two components（Pd@PtNAs with 36.9 wt%and 55.2 wt%Pt）by adjusting the atomic ratio of Pd and Pt.The results of ORR and methanol oxidation reaction（MOR）show that the Pd@PtNAs（36.9 wt%Pt）have the admirable electrocatalysis performance than Pt/C.This method provides a new idea for the design and synthesis of Pd@Pt core-shell nanomaterials with nanodot arrays on the surface.2.Three-dimensional PdSn alloy nanochain networks（3D PdSn NCNs）were synthesized by a simple and mild method.3D PdSn NCNs were synthesized by reducing Na₂PdCl₄ and SnCl₂ with active sodium borohydride（NaBH₄）at room temperature with the sodium citrate and KBr as capping agents.Three different components of 3D PdSn NCNs(3D Pd₇₅Sn₂₅5 NCNs,3D Pd₅₆Sn₄₄4 NCNs and 3D Pd₂₈Sn₇₂2 NCNs)were synthesized by adding different proportions of metal precursors.The result of electrocatalytic ethanol oxidation reaction（EOR）shows that 3D Pd₂₈Sn₇₂2 NCNs has the highest catalytic activity and stability.The mass activity of 3D Pd₂₈Sn₇₂2 NCNs for EOR is 4.53 times higher than that of commercial Pd/C.This method provides a new design idea for the synthesis of Pd-based alloy catalysts with excellent properties.3.By combining dendritic PdCuCo alloy crystals with amorphous Ni-B,the composite with highly dispersed active surface was formed.Compared with pure PdCuCo alloy,the electrocatalytic activity of the composite was significantly improved.The effects of different thickness of Ni-B film were studied through ORR and MOR test.The results showed that PdCuCo/Ni-B coated with different thickness of Ni-B film exhibited a Gauss-like distribution for electrocatalytic activities.In addition,for ORR,the specific activity of PdCuCo/Ni-B-2 is 3.3 times that of PdCuCo,while for MOR,the specific activity of PdCuCo/Ni-B-3 is 4.1 times that of PdCuCo.This indicates that the interfacial effect between Ni-B and PdCuCo alloys plays a significant role in enhancing the electrocatalytic activities.This study can provide ideas for the design of composite materials formed by the combination of Pd-based crystals and amorphous.