Catalytic Performance Of Pd-based Catalysts Regulated By Size And Support For Oxygen Reduction Reaction

Proton exchange membrane fuel cell(PEMFC)is one of the most likely candidates to replace traditional energy sourcesin the future due to its greenness,cleanliness and high-efficiency.However,the depressed cathodic oxygen reduction reaction(ORR)kinetics is the main reason limiting the development of fuel cells.Pt-based catalysts are considered to be the most effective ORR electrocatalysts,but large-scale commercialization of fuel cell catalysts has been difficult to develop due to the high cost and low stability.Pd has an electronic structure and lattice constant similar to Pt,and is relatively cheap.However,compared with Pt,its catalytic activity still needs to be further improved.The intrinsic activity of the catalyst is closely related to its electronic structure.Therefore,the electronic structure of Pd-based catalyst can be adjusted by optimizing the surface composition and surface structure of the catalyst,thereby improve the electrocatalytic performance of Pd-based catalyst.In this dissertation,the application of Pd-based catalysts in ORR was studied by changing morphology and support modification.The electronic structure,surface composition and surface structure of Pd catalyst were adjusted through some strategies,such as producing defects,doping and size effect,so as to achieve a significant improvement in the electrocatalytic performance of Pd-based catalytic.The main contents of the research are as follows:1?Pd-Ni ellipsoidal nano-alloy catalyst with long diameter of 5±0.1nm and short diameter of 3±0.1nm supported on carbon black was successfully synthesized via a facile one-pot synthesis route.Duringthesyntheticprocess,cetyl trimethyl ammonium chloride(CTAC)wasusedas a structure directingagent,which induced the elliptical morphology and modified the surface Pd 3d electronic structure through interfacial coupling interaction.The addition of Ni to Pd can significantly accelerate the catalytic activity,which is caused by the structure of the active site,electron distribution and size effect.Compared with traditional Pt/C,Pd/C and Pd-Ni nanoparticle catalysts with no specific morphology supported on carbon black(Pd-Ni/C NS),Pd-Ni/C ES demonstrate both ultrahigh ORR activity and favorable long-term durability in alkaline solutions.Density functional theory(DFT)calculation results show that at 0.85 V(vs reversible hydrogen electrode(RHE)),the free energy diagram of the ORR on Pd-Ni/C ES exposed(111)crystal facet is closer to the ideal path than that of the Pd-Ni/C NS,suggesting that the ORR process over Pd-Ni/C ES is easier than that over Pd-Ni/C NS catalysts.2?The Ti₄O₇ submicron particles with abundant defects were prepared by ball milling treatment and used as a support material to load Pd nano-particles(Pd NPs).The electrocatalytic performance of this catalyst(Pd/Ti₄O₇(F))towards ORR was investigated.It was found that as compared with Pd NPs supported on commercial Ti₄O₇(Pd/Ti₄O₇(C)),Pd/C and commercial Pt/C,the Pd/Ti₄O₇(F)catalysts exhibitedthe best catalytic activity and excellent durability in alkaline solution.According to X-ray photoelectron spectra(XPS),electron paramagnetic resonance(EPR)spectra and conductivity measurement results,thestrong metal-support interactions(SMSIs)and high conductivity induced by abundant oxygen vacancies and disorder layers in the treated Ti₄O₇ support play a vital role in promoting the ORR activity of this electrocatalyst.These provide a new strategy for the design of high-performance ORR catalysts.