The Synthesis Of Low-Load Noble Metal Alloy Eletrocatalysts And The Study Of Its Oxygen Reduciton

The main obstracle of the commercial development for fuel cells is the cathodic oxygen reduction reaction.（ORR）Currently there is no systematic theory to shed light of the sluggish kinetics of ORR.One kind of significance is to develop catalysts with high-efficient ORR activity.In this thesis the primary work is focused on the two methods of catalyst synthesis based on the strategy of self-catalyzed method,that is preparation of Pd-based core-shell structure and boron-doped Pd-based interstitial nanoalloy（B-Pd）for ORR.The detail of those studies is blow.In chaper 3,Pd-based core-shell structures with different component were synthesized by the favour of formic acid oxidation on Pd,such as Pd₃@Pt₂/C,Pd₃@Pt₂Au_0.1/C,Pd₃@Pt₂Ag_0.1/C,Pd₃@Pt₂M_0.67/C.Pd₃@Pt₂/C showed enhanced ORR performance with a mass and special activity of 0.339 A/mg _Pt and 0.382m A/cm² at 0.9 V,which was 3.4 and 3.3 times of that of commercial Pt.It suggested that Pd₃@Pt₂Au_0.1/C had a better CO-resistance that Pd₃@Pt₂/C in spite of its lower activity.A deep study about the different deposition trend of Pt and Au atom on Pd core was investigated.The result was even differently.It indicated that Pt atom could shaped a well-coated shell on Pd involved two steps that were island-like deposition of Pt atom and the diffusion of Pt island to evolve to the fine Pt shell.The case of Au atom is that it could only deposit onto Pd to form a structure of Au island.By the comparation of deposited mode of Pt and Au atoms,we suggested that the diffusion of Pt atom was induced by tha active H atoms in-situ generated in the decomposition of formic acid.A study of the synthesis of B-Pd in NaBH₄-DMF system was conducted.The biggest advantage of the method was that Na BH₄ was acted as the reductant and B-dopant which used to be borane-organics compound.Na BH₄ could be dissociated to Na⁺and BH₄^-,BH₄^-was stable in DMF and could be decomposed into B atoms that can penetrate into the lattice of Pd.As-synthesized B-Pd/C exhibited extremely high ORR activity with a mass and special activity of 0.97 A/mg _Pt and 1.27 m A/cm² at 0.9V in base,which was 14 and 14.6 times of that of commercial Pt.Combine the result of CV test and DFT calculations,three active sites were uncovered in B-Pd/C.The first one was B_S-Pd（S denotes sublayer）showing good activity and stability.The second one was the structure（Pd-BO_X）-Pd（X is 2 or 3）with extraordinary activity but with poor stability.The last one was Pd-BO₂ with comparable activity of Pt.this structure was a totally new non-metallic site may approach to novel designing of ORR catalyst.The APEFC performance of B-Pd/C was tested,showing a peak power density of 750 m W/cm²,with a loss of 250 m W/cm² than that of commercial Pt.The contradiction of result between the APEFC and RDE test suggested that RDE had its limition in the estimation of catalyst overall performance.It indicated that more possible influances related to fuel cell should be taken into account.The study in chaper 4 presented that B-doped Pd alloy had a great potential tobe high-efficient catalysts.We investigated the ORR property of B-Pd Au in acid considering different factors.Electrochemical tests indicated B-Pd₁₀Au₁/C had much better activity than Pd/C with an overrun of 70 m V on half-wave potential.The mass activity at 0.9 V is 0.12 A/mg _Pd,with an enhanced factor of 10 to that of Pd/C.At 0.85V,its mass activity is 0.66 A/mg _Pd as same as that of Pt.The PEMFC performance of B-Pd₁₀Au₁/C was tested with a peak power density of 1050 m W/cm²,having a shrink of 500 m W/cm² compared with Pt.Despite of this,B-Pd₁₀Au₁/C shows its potential in application.