Structure Designing Of Pt/Pd Based Catalyst And Their Performance For The Oxygen Reduction Reaction

Rational design of catalysts toward oxygen reduction reaction(ORR)is of great importance for the development of fuel cells.Ordered intermetallics show enhanced activity and structural stability due to the regular atom arrangement in their crystal and which have received widespread attention in recent years.However,there are still many problems from material preparation,performance evaluation to mechanism analysis that need to be clarified and resolved.Therefore,Pt and Pd-based alloy catalysts are explored towards ORR by introducing transition metals,optimizing morphology and structure in this dissertation.Moreover,the advanced characterization technique are adopted to investigate the structure-activity relationship of catalysts.The research contents are as follows:(1)Ordered PtFe with Pt rich surface(O-PtFe)are prepared and their performance towards ORR are greatly improved,the mass activity reaches 0.68 A mg _Pt^-1 and the activity is only 27%loss after 10,000 cycles.The strong combine of Pt and Fe atoms in the ordered PtFe structure optimized the electronic structure of Pt(improve activity)and suppressed the dissolution of Fe atoms(improve stability).The in-situ XAFS experiment directly reveals that the ordered structure in O-PtFe not only reduces the binding strength of HO*on the Pt surface,but also promotes the leaching resistance of Fe and suppresses their dissolution.(2)Ultrathin Pt₃Ni bimetallic alloy nanowires(Pt₃Ni BANWs)are obtained by rationally introducing Ni(acac)₂ as well as adjusting the polarity of reaction solvent.Due to the integration of multiple compositional and structural advantages,the as-prepared Pt₃Ni BANWs deliver higher mass activity than Pt NWA and Pt.Pt Cu nanoframes which deliver enhanced activity while dissatisfied durability towards ORR are prepared by one-pot strategy.To further promote their performance,L1₁-Pt Cu with rhombohedral structure is obtained by high temperature treatment.The durability of ordered Pt Cu has been strengthened but the initial activity(0.44 A mg _Pt^-1)is decreased due to the particles aggregation.Moreover,an in-situ heating experiment assisted by 3D chemical sensitive tomography technique was utilized to visualize the structural evolution of the PtCuNFs during heating process.It reveals that the atomic migration induced by high temperature accelerates the formation of structurally ordered intermetallics meanwhile results in the collapse and aggregation of the nanostructures.(3)Structurally ordered PdFe intermetallic are obtained by decomposing of acetate salt precursors and the ordered PdFe deliver enhanced ORR performance than disordered PdFe.To further improve the performance of PdFe intermetallics,a dealloying and decoration strategy is conducted to fabricate Pt decorated porous PdFe intermetallics.As expected,p-o-PdFe@Pt exhibits significant enhancement in both activity and durability.Moreover,3D tomography technique was conducted to visualize the structural and compositional evolution of p-o-PdFe@Pt after cycles.The tomographic reconstructions and CO-striping experiments prove that the gradual Pt enrichment on the surface is pivotal to enhance their activity as well as durability.PdFe@C_HP nanoreactors are prepared by sacrificice template strategy to place the nanoparticles in internal surface of hollow carbon shell.The optimized PdFe@C_HP-m nanoreactors show enhanced stability(only 4.4%activity loss)in comparison to Pt/C(40%loss)in 0.1 M HCl O₄ after 20,000 cycles.In addition,more active sites are exposed due to the carbon layer corrosion and the removal of residual Si O₂ in 0.1 M KOH electrolyte,the activity of PdFe@C_HP-m even increased by 2.6 times after 50,000 cycles.