Controlled Synthesis Of Pt-based Multi-metallic Nanocrystals For Methanol Oxidation Reaction

Direct methanol fuel cells?DMFCs?have received great attention in recent years because of their environmental protection and energy saving advantages,including high energy conversion efficiency,simple structure and low pollutant emission.Among them,Pt is the most widely used monometallic catalyst for methanol oxidation reaction?MOR?in practice applications.However,the high price,limited abundance,and low resistance to CO poisoning of Pt severely restrict its widespread usage in DMFCs.In this dissertation,we focus on a series of studies on the enhancement in catalytic activity,stability and anti-toxicity of Pt-based nanocrystals.For this purpose,designing ternary Pt-based alloy nanocrystals with a dendritic structure is highly desirable.Here,PtPdCu alloy hexapods and PtCuRh alloy nanodendrites were generated by one-pot approach and their use as catalysts for MOR.The main innovative results are summarized as follows:?1?We have successfully synthesized PtPdCu alloy hexapods by a wet chemical method at 200°C with oleylamine and dimethylformamide?DMF?as reducing agents.By varying the amount of the Pt precursor fed in the synthesis,the atomic ratio of Pt,Pd and Cu was tuned.As such,three kinds of ternary alloy hexapods including Pt₂PdCu₄,Pt₃PdCu₄ and were produced.Compared to commercial Pt/C,the Pt-based ternary hexapods exhibited the substantially enhanced catalytic activity and stability for MOR.Among them,the Pt₅PdCu₅ hexapods showed the highest mass(0.97 mA/?g_Pt)and specific?7.39 mA/cm²?activities towards MOR,which were 5.4 and 19.4 times higher than those of commercial Pt/C,respectively.This enhancement can be attributed to the ligand effect and bifunctional mechanism arising from the introduction of Pd and Cu.In addition,the rich active sites on the hexapods are also responsible for the enhancement in the catalytic activity.?2?The PtCuRh nanodendrites were prepared by one-pot approach at 200°C using oleylamine and DMF as reducing agents.Compared to commercial Pt/C and PtCu nanodendrites,the PtCuRh nanodendrites exhibited the substantially enhanced catalytic activity and stability for MOR.Specifically,the PtCuRh nanodendrites showed the excellent mass activity(1.07 mA/?g_Pt)and specific activity?1.91 mA/cm²?,which were7.95 and 6.29 times higher than those of commercial Pt/C,respectively.This enhancement can be attributed to the bifunctional mechanism arising from the introduction of oxyphile and stable Rh.