Study On Platinum-based Anodic Electrocatalysts For Direct Methanol Fuel Cells

Direct methanol fuel cells (DMFCs) have received more and more attention in electric vehicles and portable devices due to the merits of methanol (such as high energy density, low contamination, easy storage and transportation). However, the high cost and low electrocatalytic activity of the current catalysts are the key obstacles to restrict the widespread application of fuel cells. Nowadays, people manage to increase the catalytic activity and utilization of catalysts, and decrease the consumption of noble metal Pt as key goal for DMFCs. A lot of resarch shows one of the main ways to achieve this goal is to disperse noble metal nanoparticles uniformly on carbon supports with excellent conductivity and large specific surface area.In this paper, we used carbon nanotubes and graphene as catalyst carrier and developed different synthetic methods to realize small size and high dispersity of noble metal nanoparticles deposited on the carbon materials surface. The morphology, structure and electrocatalytic performances of the prepared materials towards methanol oxidation were investigated by different methods. The main points of this thesis are summarized as follows:(1) Taking β-cyclodextrin (β-CD) functionalized CNTs as supports, β-CD as reductant of metal ions and dispersant of CNTs, PtRh/β-CD-CNTs catalysts with different atomic ratio of Pt/Rh (npt/nRh) were prepard by one-pot hydrothermal method. The structure, composition and morphology of the obtained PtRh/β-CD-CNTs hybrids were characterized by different methods, the electrocatalytic performance and stability of synthetic catalysts for methanol oxidation were investigated on electrochemical workstation. The results indicate that P-CD is in favour of obtaining PtRh nanopartieles with high dispersity and small size by in-situ reduction method. The electrochemical tests demonstrate that the Pt1Rh1/β-CD-CNTs catalysts exhibit excellent electrocatalytic performance.(2) Taking anionic polymer poly(sodium-4-styrenesulfonate) noncovalent functionalized CNTs (PSS-CNTs) as supports, Pt-CeO2/PSS-CNTs with different atomic ratio of Pt/Ce (npt/nce) were prepared. The structure, component and micromorphology were characterized by Raman spectrum, X-ray diffraction (XRD), energy dispersive X-ray spectrometer (EDS) and transmission electron microscopy (TEM), respectively. Taking the Pt-CeO2/CNTs and E-TEK PtRu/C catalysts as control samples, the electrochemical performance of catalysts torwards methanol oxidation were measured by CV and CA, TEM results show that Pt nanoparticles coated on the surface of PSS-CNTs have better dispersity and smaller average diameter than that of pristine CNTs. Comparing with Pt-CeO2/CNTs and E-TEK PtRu/C catalysts, Pt-CeO2/PSS-CNTs with npt/nCe ratio of 2/3 exhibits higher catalytic activity and stability for methanol electrooxidation.(3) Taking graphene as carbon support, we first prepared nanorods/Graphene hybrids by simple hydrothermal method. Then hybrids catalysts were synthesized by microwave-assisted ethylene glycol reduction process. The morphology and structure of the catalysts were investigated by XRD, TEM, EDS. CV and CA were used to measure the electrocatalytic activity and stability of catalysts for methanol oxidation. Compared with Pt/GNs and E-TEK PtRu/C catalysts, Pt/Mn3O4/GNs catalysts exhibit larger electrochemical surface area (ESA), higher mass specific activity, surface specific activity and electrochemistry stability for methanol oxidation due to the synergetic effect of Pt and Mn3O4.