| Currently, platinum-based and palladium-based multi-metal nano-catalysts are still the main research aspects of the fuel cell anode catalyst. Among them, PtAu and PdAu binary catalysts have attracted widespread attention till now. Studies show that there exist synergistic effect, electronic effect, bifunctional effect and third body effect between the elements, which greatly enhance the activity and stability of platinum-based and palladium-based catalysts, and prolong the life by preventing the CO adsorption on catalyst surface. In this thesis, we add another element Cu, which is prone to be etched in the sulfuric acid solution (dealloying), based on the synergistic effect of PtAu or PdAu. The resulting catalysts not only improve their specific surface area, but also possess a unique spatial structure, namely core-shell structure. In addition, the catalyst performance can also be affected by supports. Combining graphene with carbon nanotubes, which have a bigger specific surface area and better conductivity, would provide additional surface area, ease aggregation of supports, cause interaction and finally improve utilization of noble metal. Meanwhile, active sites distributed on the surface of graphene and synergistic effect between noble metal can also enhance the electro-catalytic activity of alcohol. The main contents are as follows.Firstly, a series of carbon nanoparticles supported platinum-based catalysts are prepared by liquid phase reduction method using sodium borohydride as reducing agent. Controlling the atomic ratio of Pt and Au to be 1:1, simultaneously, the content of Cu is gradually increased. The as-prepared catalysts are activated by electrochemical cyclic voltammetry in the solution of 0.5M sulfuric acid. With the continuous dissolving of Cu from catalyst surface, it gradually evolves into a typical core-shell structure with a precious metal enriched surface. When analyzed the catalysts before and after activating by XRD, EDX, TEM, XPS and CV testing methods, we have found that the leaching of large amount of Cu triggers the re-arrangement of Pt/Au atoms on the surface of the metal nanoparticles, which could maximize the use of noble metals. On the other hand, the contribution from the synergistic effect such as the Cu-depleting induced geometric (lattice mismatch, strain, defects and/or dislocations) effect and/or electronic modification effect should be the other important factor for the formation of PtAuCu (core)-PtAu (shell) structure. The higher the Cu content is in the precursor, the lower the residual buried-underneath Cu atoms retain after the activation. Because a large amount of Cu contents in the nanoparticle may provide sufficient dissolution (dealloying) channels, favoring the depletion of Cu into the electrolyte. Therefore, the activated Pt10Au10Cu80/C exhibits the best catalytic performance for the electro-oxidation of commonly-targeted small organic molecule fuels.To further improve the performance of the anode catalysts, we design a rGO-CNT nano-composite with three-dimensional microstructures obtained by hydrothermal treatment as supports. Pd/rGO-CNT, PdAu/rGO-CNT, PdAuCu(10%)/rGO-CNT, PdAuCu(30%)/rGO-CNT and PdAuCu(50%)/rGO-CNT nano-catalysts are also prepared by liquid phase reduction method. Experiments show that the formation of macroscopic rGO-CNT via π-π stacking, hydrogen bonding and electrostatic interaction can effectively prevent aggregation between graphene layers, enlarge active surface area and promote metal nanoparticles attach on the supports more uniformly. In addition, the formation of core-shell structure after dealloying may increase active sites that significantly ameliorate catalytic properties for alcohols in alkaline circumstance. Certainly, we also discover that Pd-based catalysts behave a more excellent performance for ethanol than methanol by the means of electro-chemical cyclic voltammetry and electro-chemical impedance spectroscopy. |
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