新型氧还原电催化剂的制备及性能研究

发布时间：2018-05-25 16:43

本文选题：质子交换膜燃料电池 + 氧还原反应　；参考：《中国矿业大学》2017年硕士论文

【摘要】：在质子交换膜燃料电池(PEMFCs)中,铂是已知最佳的氧还原反应(ORR)催化剂,但是其缓慢的氧还原动力学、有限的存储和高昂的价格严重阻碍了PEMFCs的商业化。因此,低铂甚至是非铂ORR催化剂被广泛研究。最近研究表明,核壳结构不但降低了催化剂的铂载量,而且提高了ORR活性。氮掺杂的碳基催化剂在ORR方面也展现出优异的活性和稳定性。本论文根据表面偏析的原理,制备过渡金属氮化物为核,铂为壳的核壳结构ORR催化剂。结合物性表征和电化学表征的结果,分析催化剂中铂壳层厚度和核纳米粒子对氧还原催化性能的影响,阐明相关的催化机理,以期掌握核壳催化剂的结构调控方法,开发出高效稳定且廉价的PEMFCs催化材料。主要研究内容如下:(1)通过浸渍还原法制备了初级产品,然后在氨气中退火处理,最后在酸溶液中采用电化学去合金法得到一系列的N-Fe M@Pt/C(M=Mo、V、W)核壳催化剂。(2)通过调节前驱体中各元素的摩尔比来制备不同铂壳层厚度的催化剂,并采用循环伏安法及线性扫描伏安法评价其催化性能。结果显示,随着铂壳层厚度的减小,催化剂的电化学比表面积和质量活性(0.9V vs.RHE)逐渐增加。相对于商业Pt/C而言,本论文制备的所有催化剂在质量活性上都大幅提高,特别是N-Fe_5Mo_1@Pt_3/C催化剂,它的质量活性甚至达到Pt/C的18.9倍。(3)通过调节元素种类制备了不同核纳米粒子催化剂,并研究了5000圈循环伏安扫描前后的ORR稳定性。结果表明,它们初始的ORR活性顺序为N-Fe_5Mo_1@Pt_3/CN-Fe_5V_1@Pt_3/CN-Fe_5W_1@Pt_3/C。在5000圈循环扫描之后,所有催化剂的ORR活性都有所退化,但相比于初始的Pt/C依旧展现出更高的活性。ORR活性退化的原因有两种:一是金属粒子的团聚或脱离;二是不断的循环伏安扫描后,由电化学去合金法产生的空位被附近的铂原子填充。
[Abstract]:In proton exchange membrane fuel cell (PEMFCs), platinum is the best known catalyst for oxygen reduction, but its slow oxygen reduction kinetics, limited storage and high price seriously hinder the commercialization of PEMFCs. Therefore, low platinum and even non-platinum ORR catalysts have been widely studied. Recent studies show that the core-shell structure not only reduces the platinum loading of the catalyst, but also improves the ORR activity. Nitrogen-doped carbon-based catalysts also showed excellent activity and stability in ORR. In this paper, based on the principle of surface segregation, a core-shell structure ORR catalyst with transition metal nitride as core and platinum as shell was prepared. Based on the results of physical and electrochemical characterization, the effects of platinum shell thickness and nuclear nanoparticles on the catalytic performance of oxygen reduction were analyzed, and the related catalytic mechanisms were elucidated in order to master the structural control methods of core-shell catalysts. A high efficient, stable and cheap PEMFCs catalytic material was developed. The main research contents are as follows: (1) Primary products were prepared by impregnation reduction method and then annealed in ammonia gas. Finally, a series of core-shell catalysts with different thickness of platinum shell layer were prepared by adjusting the molar ratio of the elements in the precursor by electrochemical dealloying method in acid solution. The catalytic performance was evaluated by cyclic voltammetry and linear scanning voltammetry. The results showed that the electrochemical specific surface area and mass activity of the catalyst increased with the decrease of the thickness of platinum shell. Compared with commercial Pt/C, the mass activity of all the catalysts prepared in this paper is greatly improved, especially the mass activity of N-Fe_5Mo_1@Pt_3/C catalyst, which is 18.9 times higher than that of Pt/C. The stability of ORR before and after 5000 cycle cyclic voltammetry scanning was studied. The results show that their initial ORR activity is in the order of N-Fe5MoM\ ORR\ After the 5000 cycle scanning, the ORR activity of all the catalysts degenerated, but there were two reasons for the degradation of the activity of ORR than that of the initial Pt/C: the first was the agglomeration or detachment of metal particles; Second, after continuous cyclic voltammetry, the vacancies produced by electrochemical dealloying are filled with nearby platinum atoms.
【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36;TM911.4

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