| Fuel cell is a kind of ideal power source to suit for the future energy and environmental requirements, and its prospective application involves clean power generation, transportation,space navigation. However, low oxidation activity of formic acid and high cost of Pt-based catalysts are the major drawbacks to limit the DFAFC's practical application. Therefore, considerable efforts have been focused on the exploration of less expensive, more abundant non-platinum catalysts with enhanced performance. In the preparation of catalysts on the supports, one of the significant challenges is how to deposit metal nanoparticles uniformly on the surface of them due to their inherent inertness. In order to anchor and deposit catalyst nanoparticles on the surface of the supports, we modified the surface of support, which could increase the electrocatalytic activity and utilization ratio of catalyst.Pd catalyst was found to possess superior performances in formic acid oxidation compared with Pt-based catalysts. In addition, as the amount of Pd is much more abundant on the earth than that of Pt, it is considered as substitute of Pt for catalyst in DFAFC. Surface modification of carbon supports was carried out by many kinds of additives with different functional groups, such as N element, hydroxyl (–OH), carboxyl (–COOH) groups. Their influence on the catalysts'morphology, partical size and the electrical properties was studied. The main contents of the thesis are following:Firstly, not only the current research of the fuel cell , the progress of catalyst and catalyst support were given, but also the current questions about the fuel cell catalyst, objective and the main research contents of this paper were described in detail.Secondly, MWCNTs modified with -OH functional groups of different additives were used as composite supports for synthesizing nanostructured palladium catalysts for formic acid oxidation. The selected additives contain HP-β-CD, Chitosan, Glycol, Catechol and so on. And the influence of the additives on the catalysts'morphology, partical size and the electrical properties was studied. The results suggest that palladium nanoparticles can be deposited on the surface of MWCNTs, and have the trendency to further reunion to cluster-like structures at the presence of the -OH functional groups. The activity order of palladium catalyst in H2SO4 is as follows: HP-β-CD > catechol > Chitosan > ethylene glycol. And the activity for formic acid oxidation is in sequence as follows: HP-β-CD > catechol > ethylene glycol > chitosan. Furthermore, the reason of activity order was discussed from the perspective of the molecular structure.Thirdly, sodium citrate, sodium oxalate, phthalate and sodium alginate were used as additives to modified MWCNTs, all of which contain -COOH functional groups. Then the formed compositions were used as supports of nanostructured palladium catalysts for formic acid oxidation. The influence of different structured additives on the catalyst morphology, particle size and electrocatalytic activity were studied. The results suggest that on the effect of the -COOH functional groups, palladium nanoparticles can be deposited on the surface of MWCNTs, and have the trendency to further reunion to cluster-like structures. The order of the particle size is as follows: sodium citrate≈sodium oxalate < phthalate < sodium alginate; the activity order: citrate > oxalate > sodium alginate > phthalate; and stability order: phthalate > citrate > sodium alginate > oxalate.Fourthly, we prepared highly dispersed palladium nanostructured catalyst with MWCNTs as supports, which was modified by the phen, ppy, PANI, en etc, respectively. The influence of the additives on the catalysts'morphology, partical size and the electrical properties was studied. The results showed that the palladium nanoparticles were well-dispersed on the surface of MWCNTs with a relatively narrow particle size distribution at the presence phen or ppy, and the electrocatalytic activity increased significantly. On this basis, to further improve the catalytic activity, we prepared hollow nanospheres catalyst Pd/ppy-XC-72 and Pd/ppy-MWCNTs. In the preparation progress, Co nanoparticles as sacrificial templates were deposited on the prepared polypyrrole-carbon composites by chemical reduction, and then Pd hollow nanospheres formed through the surface replacement reaction between the surface of Co nanoparticles and PdCl2 at room temperature. The catalysts of hollow structure Pd showed a very high electrochemically-active surface area and significant increase in electrocatalytic activity towards formic acid oxidation, which make them the preferable catalysts for direct formic acid fuel cells (DFAFC).Fifthly, the composite of additive-modified C60 was introduced as a new type of support of nanostructured palladium catalysts for formic acid oxidation. The additives included ppy, HP-β-CD and sodium citrate. The influence of different structured additives on the catalyst morphology, particle size and electrocatalytic activity were studied. The results show that the functionalized C60 composite support can control the particle size and increase dispersivity, and different functional groups can lead to different morphology. The uniform and well-dispersed Pd nanoparticles can be obtained on ppy-modified C60, while the Pd nanocluster catalysts were prepared at the presence of HP-β-CD or sodium citrate. The results were consistent with that with MWCNTs as support. The order of the particle size is as follows: ppy HP-β-CD > sodium citrate. Furthermore, because of the special structure and strong adsorption capacity to metal, the C60 may increase the metal loading. Therefore, the ppy-C60 catalyst may be a kind of more promising catalyst. The electrocatalytic activity of the as-prepared Pd/ppy-C60 catalysts for the oxidation of formic acid is much higher than those of others, showing that the ppy-C60 may be a better potential candidate to be used as the supports of catalyst for electrochemical oxidation.Sixthly, we summarized the above studies to explore the influence law of different additives and supports on the formation and catalytic properties of the catalysts.
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