| To satisfy the increasing demand for energy and solve the environmental problems caused by the burning fossil fuels, the development of sustainable and renewable green energy becomes hot topics in the field of energy. Direct methanol fuel cells(DMFCs) has advantages of high energy conversion efficiency, low carbon emissions and convenient fuel storage and transportation, which has favorable development foreground in the application of vehicle and portable devices. However, the poor kinetics of methanol electro-oxidation result in decrease in cell efficiency. Therefore, the development of anode catalysts with highly catalytic performance to improve the cell efficiency is in urgent need. With efficient catalytic performance to methanol oxidation, platinum has been most widely used as anode catalysts in DMFC. However, the expensive cost for Pt, Pt surface poisoning by CO molecules, and Pt nanoparticles(NPs) aggregation after a long-term catalytic reaction would deteriorate the catalytic efficiency for the electro-oxidation of methanol.From the perspective of effectiveness and commercialization of Pt-based catalysts, this paper is mainly focused on the improvement of catalytic activity of Pt catalyst for methanol electro-chemical oxidation by adding the second component nickel(Ni) and by changing the atomic ratio of Pt to Ni to explore the effects of electron transfer between different metals on catalytic activity. The main content includes the following sections:Firstly, with room temperature ionic liquid-assisted sputtering deposition procedure, we prepared metal NPs supported on multi-walled carbon nanotubes(MWCNTs) hybrids. This method is free of polymers and surfactant stabilizers, and without any surface treatment or modification to MWCNTs. Meanwhile, it is flexible to prepare a variety of hybrids through changing the target materials.Secondly, a series of characterizations have been carried out to obtain the morphology structure, elements chemical valence and electronic structure of as-prepared hybrids by using transmission electron microscopy(TEM), high-resolution transmission electron microscopy(HRTEM), X-ray powder diffraction(XRD), X-ray photoelectron spectroscopy(XPS) and X-ray absorption near edge structure(XANES) etc. These characterization provides important information for analyzing the catalytic performance.Finally, the catalytic activity and the long term cycle stability of as-prepared hybrids for methanol electro-oxidation have been investigated. The experimental results show that the introduction of the second component Ni plays an important role for the promotion of catalytic activity and stability of Pt. Among the as-prepared hybrids, we found the PtNi alloy NPs-MWCNTs hybrids with the atomic ratio of Pt to Ni is 1:1 has the best catalytic effect for methanol electro-oxidation. And we attempted to verify and study the strong force between Pt and imidazoles ionic liquids, as well as its effect on catalyst performance. Besides, we also prepared the non-platinum catalyst, single metal Ni NPs-MWCNTs hybrids, and studied its catalytic activity for methanol electro-oxidation.The experimental results in this work suggested that the room temperature ionic liquid-assisted sputtering deposition method has the advantages of simple preparation process, free of byproducts and no-addition of stabilizers, compared with chemical method. With this method, the atomic ratio of Pt to Ni could be controlled simply, a variety of hybrids could be prepared flexibly. The results of catalytic tests showed that for methanol electro-oxidation, the as-prepared PtNi alloy NPs-MWCNTs hybrids have high catalytic activity, and single metal Ni NPs-MWCNTs hybrids also have a certain extent of catalytic activity for methanol electro-oxidation. The characterization results showed that the synergistic effect of bimetal—Ni could participate in the catalytic process and modify the electronic structure of Pt, greatly improve the catalytic performance of PtNi alloy hybrids. |
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