炭载钯基催化剂的制备及氧还原性能研究

发布时间：2018-08-13 13:17

【摘要】：燃料电池是一种高效、环保的发电装置,在分布式发电、电动汽车等领域具有广阔的应用前景。但目前使用的Pt基氧还原(ORR)催化剂用量大、成本高,严重制约了燃料电池的商业化进程。因此,研究开发高效、低廉的ORR催化剂具有极其重要的意义。Pd基催化剂由于具有较高的ORR活性和相对较低的价格,被认为是最有潜力替代Pt基催化剂的金属基ORR催化剂。本论文设计并制备了碳纳米管担载PdFe合金催化剂(PdFe/CNT)、超晶格PdFe/CNT以及表面富Pt的PdFePt/CNT催化剂,探究了催化剂组成与结构对ORR性能的影响规律。主要结论如下:首先,采用NaBH4辅助乙二醇还原共沉积法制备了 PdFe/CNT合金催化剂,研究了制备体系pH值、制备体系温度、Pd/Fe比对催化剂形貌与晶型结构的影响机制。结果表明,适当比例的Fe与Pd形成合金产生了电子效应和几何效应,促进了 ORR活性的提高。制备的Pd_(75)Fe_(25)/CNT催化剂具有最佳的ORR催化活性与极高的抗甲醇性能及电化学稳定性,其在酸性及碱性介质中半波电位分别比Pd/CNT催化剂提升了 8 mV与14 mV。为了进一步提升ORR活性,采用热处理方法诱导Pd50Fe50/CNT催化剂调变合金结构,制备了L10型超晶格PdFe/CNT催化剂。结果表明,经超晶格结构转变后,PdFe/CNT催化剂的ORR半波电位提升了 69 mV,ORR质量活性提高了 4.6倍(0.81Vvs.RHE)。此外,超晶格PdFe/CNT催化剂表现出优良的抗甲醇能力,是一种具有高选择性的ORR催化剂。最后,通过对Pd_(75)Fe_(25)/CNT催化剂进行表面原子置换,制备了表面富Pt的PdFePt/CNT三元催化剂。结果表明,制备的催化剂Pt担载量仅为7.05wt%,但ORR活性与稳定性均优于商业20%Pt/C,其在酸性介质中起始电位和半波电位为0.948 V和0.861 V,分别比商业Pt/C高出9 mV与20mV。这一方面是由于表面富Pt的结构极大地提高了 Pt的利用率;另一方面,Pd、Fe、Pt间的电子电荷转移和应变效应修饰了表层Pt原子的电子结构,改善了 ORR过程中的Pt-0吸附强度,从而加快了 ORR反应。
[Abstract]:Fuel cell is an efficient and environmentally friendly power generation device, which has a broad application prospect in distributed power generation, electric vehicles and other fields. However, the large amount of Pt-based oxygen reduction (ORR) catalyst and the high cost have seriously restricted the commercialization of fuel cells. Therefore, the research and development of high efficiency and low cost ORR catalysts is of great significance. Due to their high ORR activity and relatively low price, PD based catalysts are considered to be the most potential metal-based ORR catalysts to replace Pt based catalysts. In this paper, carbon nanotube supported PdFe alloy catalysts (PdFe/CNT), superlattice PdFe/CNT and Pt rich PdFePt/CNT catalysts were designed and prepared. The effects of the composition and structure of the catalysts on the properties of ORR were investigated. The main conclusions are as follows: firstly, PdFe/CNT alloy catalysts were prepared by NaBH4 assisted ethylene glycol reduction co-deposition. The effects of pH value of the preparation system and PD / Fe ratio on the morphology and crystal structure of the catalyst were studied. The results show that the formation of Fe and PD alloy in a proper proportion produces electronic and geometric effects and promotes the improvement of ORR activity. The prepared PD _ (75) Fe _ (25) / CNT catalyst has the best ORR catalytic activity, high methanol resistance and electrochemical stability. The half-wave potential in acidic and alkaline media increases by 8 MV and 14 MV, respectively. In order to further improve the activity of ORR, L10 type superlattice PdFe/CNT catalyst was prepared by heat treatment to induce the structure of Pd50Fe50/CNT catalyst to adjust the alloy structure. The results show that the ORR half-wave potential of PdFe / CNT catalyst increases by 4.6-fold (0.81Vvs.RHE) after superlattice structure transformation. In addition, the superlattice PdFe/CNT catalyst exhibits excellent methanol resistance and is a highly selective ORR catalyst. Finally, Pt rich PdFePt/CNT ternary catalysts were prepared by surface-atomic substitution of PD _ (75) Fe _ (25) / CNT catalyst. The results show that the Pt loading capacity of the prepared catalyst is only 7.05 wt. but the activity and stability of ORR are superior to those of commercial 20Pt / C, the initial potential and half-wave potential in acidic medium are 0.948 V and 0.861 V, respectively, which are 9 MV and 20 MV higher than commercial Pt/C. On the other hand, the electronic charge transfer and strain effect between PdFeN Pt modified the electronic structure of surface Pt atoms, which improved the adsorption intensity of Pt-0 in the ORR process. Thus, the ORR reaction was accelerated.
【学位授予单位】：北京化工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36;TM911.4

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