Multi-walled Carbon Nanotubes Supported Pd-based Catalysts Synthesized By Using Dry-grinding Method

Direct ethanol fuel cell has been gaining more and more attention as one of the most promising power sources due to its many important advantages. In this thesis, the Pd based catalysts were synthesized via Dry- grinding and hydrothermal reaction proess. X-ray diffraction(XRD), scanning electro microscope(SEM) and transmissio n(TEM) were employed to characterize the morphology of the samples. Ethanol oxidation reaction was investigated on the as-prepared catalysts by using cyclic voltammetry(CV), electrochemical impedance spectroscopy(EIS) and other electrochemical test.1. Palladium(Pd) composite nanoparticles(NPs) supported on multi- walled carbon nanotubes(MWCNTs)(denoted as Pd/MWCNTs) are fabricated by a very simple process of hydrothermal reaction(HR) using the technical grade Pd O as the precursor. With a HR period of 3 h, the Pd NPs with an average size of ~5.0 nm are found to be quite uniformly dispersed on the surface of MWCNTs. The electrocatalytic activity towards ethanol oxidation reaction(EOR) for the synthesized catalysts is probed by using cyclic voltammetry(C V), chronoamperometry(CA) and electrochemical impedance spectroscopy(EIS). The 3-h prepared catalyst has demonstrated 9.5 times better EOR activity than 5-h prepared sample(151.9 m A mg-1 vs. 15.9 m A mg-1) at an applied potential of-0.24 V(vs. SCE) in the C A test. The excellent electrocatalytic activity of the 3- h Pd/MWCNTs catalyst toward EOR is mainly ascribed to its easier hydrogen evolution, lower electrode potential and the existence of Pd O as compared to other catalysts prepared.2. For the first time, it was found that dry-grinding the mixture containing technical grade Pd O and multi-walled carbon nanotubes(MWCNTs) can generate a catalyst with ultrahigh electrocatalytic activity for ethanol oxidation reaction(EOR). The as-prepared catalysts were denoted as Pd O/MWCNTs. For acomparison, the graphene and graphite supported Pd O samples were also prepared using the same process, leading to the formation of Pd O/graphene and Pd O/graphite catalysts respectively. The structural details, the morphologies as well as the particle sizes of the prepared catalysts are mainly characterized by X-ray diffraction(XRD) and transmission electron microscopy(TEM). Although no novel diffraction peaks were observed in the XRD patterns of the resulting samples, the morphologies of the samples after the dry-grinding process have changed greatly as compared to the starting materials of Pd O. The results also indicate that the Pd O/MWCNTs catalysts show the smallest particle sizes among all the prepared catalysts. The cata lytic activities of the prepared Pd O/MWCNTs catalysts towards EO R are examined by electrochemical measurements, and the results obtained from cyclic voltammery(CV) test demonstrated that the Pd O/MWCNTs catalyst delivers a forward peak current density for EOR of 5029 m A mg-1at a scan rate of 50 m V s-1, which is about 2.1 times higher than the reported value(2361 m A mg-1) obtained on the(Pd/C) catalyst. After detailed analysis, it is thought that the easier hydrogen evolution process on the Pd O/MWCNTs catalyst is regarded as the main reason for its excellent electrochemical performance as compared to other catalysts, i.e., Pd O/graphene and Pd O/graphite. Most interestingly, the as-prepared catalyst has electrocatalytic activity for both methanol oxidation reaction and formic acid oxidation, which were also explored approximately in this preliminary work.3. The synthesis of MCNTWs supported Pd C l2 catalyst was achieved by a very facile dry- grinding methond using the technical grade Pd C l2 as the precursor. All chemicals were used received without further purification. It studied the different dry-grinding time impact on the performance of the ethanol catalyzed oxidation. The results obtained from XRD test demonstrated that with enhancing the dry-grinding time, the morphologies of start materials(Pd Cl2) have changed greatly. The res ults obtained from cyclic voltammary test showed that after taking 15 min for dry- grinding process, the catalyst have showed the highest electrocatalyst active compared to other catalysts. The as-prepared Pd/MCNTWs catalysts were characterized by XRD, EDS, XPS, TEM, HRTEM, and electrochemical measurements in this work.4.The nano-catalysts of PdxNiyFez treimetallic nanoparticles(NPs, the nominal atomic ratio of Pd to N i and Fe are 1:1:1、1:1.5:1、1:1:1.5、1:1:3、1:0:3) supported on multi- walled arbon nanotubes(MCNTWs)(denoted as PdxNiyFez/MCNTWs) have been synthesized by a thermal decomposition process using temperature ionic liquids of 1-butyl-3-methylimidazolium trifluorom ethanesulfonate([BMIM]OTF) of as the solvent. After detailed analysis, it was demonstrated that the oxidation peak current on the Pd1Ni1Fe1.5/MCNTWs catalyst was about twice times higher than that on other catalysts, and the average particle size of it was the smallest one among all the samples. The results showed that Pd1Ni1Fe1.5/MCNTWs have excel ent electrocatalysis toward ethanol oxidation reaction.