Controlled Preparation Of Pd-based Electrocatalysts Based On Graphene Support And Study On Their Electrocatalytic Activity

Direct alcohol fuel cells(DAFCs) have been considered as a promising environmental friendly energy converter because of abundant fuel source, high energy density, high-energy conversion efficiency, ease of handling and low operating temperature. The alkaline DAFCs can not only effectively alleviate alcohol penetration, but also exhibit favorable reaction kinetics. Additionally, more catalysts can be employed in alkaline media. Palladium-based catalysts were discovered as highly possible candidates for catalysts in DAFCs due to their low prices, high abundance and excellent electrocatalytic activities for alcohol oxidation in alkaline environment. Graphene has been actively pursued as an electrocatalyst support due to its unusual high surface area, potential low manufacturing cost, excellent thermal and electrical properties. Despite the excellent properties of graphene, self-aggregation of graphene sheets is still a large challenge for its application and development. To address this issue, recent studies have focused on the self-assembly of graphene sheets into three-dimensional(3D) mesh structures. Ionic liquids with environmental-friendliness, strong structural design and high stability, are widely used in the functional modification of various carbon nanomaterials. The functional modification, which can effectively improve the stability and dispersion of graphene, includes non-covalent functionalization, covalent functionalization and doping functionalization. Based on the outstanding properties of ionic liquids and the graphene, in this thesis we have synthesized Pd supported on three-dimensional graphene aerogel(Pd/3DGA), Pdx Agy nanoparticles supported on three-dimensional graphene aerogel(Pdx Agy/3DGA), Pd Ag Au nanocage supported on polyionic liquids modified graphene, and the related studies on these three kinds of catalysts are as follows:(1) The Pd/3DGA catalyst has been synthesized via a simple two-step procedure involving hydrothermal synthesis and freeze-drying process. The morphology and structural properties of the resultant catalyst were characterized by SEM, IR, Raman and etc.. The electrocatalytic performances of Pd/3DGA nanocomposites were evaluated by electrochemical measurements. Research results revealed better electrocatalytic activity and stability of Pd/3DGA nanocomposites towards methanol, ethanol, ethylene glycol and isopropanol electro-oxidation in alkaline media as compared to commercial Pd/C.(2) Pdx Agy/3DGA catalysts with different composition were prepared by hydrothermal procedure, freeze-drying and co-reduction method. SEM, EDS, Raman, XRD and etc. were used to characterize the morphology and structural properties of the resulting catalysts. The electrochemical properties of the as-prepared catalysts were investigated in alkaline environment for ethanol oxidation. The electrochemical experiments showed that Pd1Ag1/3DGA exhibited the best electrocatalytic activity and stability.(3) The polyionic liquids(1-vinyl-3-acetonitrile imidazolium bromide) prepared by in-situ polymerization have been used to modified graphene via surface functional modification to get PIL-G support. The porous Pd Ag Au nanocages synthesized through galvanic replacement were load on PIL-G to obtain Pd Ag Au/PIL-G catalyst. The morphology and structure of Pd Ag Au/PIL-G were characterized by SEM, EDS, UV-vis and etc.. Research results revealed that catalyst exhibited significantly superior activity and stability after the support was modified by PIL.