Pt-Co合金纳米催化剂制备及催化性能研究

发布时间：2018-03-05 02:00

  本文选题：Pt-Co合金纳米催化剂　切入点：表面偏析　出处：《昆明理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：燃料电池是最受关注、推崇的新型绿色清洁能源之一。燃料电池由于工作运行温度低、启动速度快、功率密度高和环境污染低,被看做新一代最环保的绿色动力能源转换装置。但由于Pt资源的稀缺,使得Pt基催化剂的成本居高不下,制约了质子交换膜燃料的发展和推广,进而使燃料电池不能进行大规模商业化应用。在燃料电池商业化过程中,提高催化剂的催化性能和降低Pt的用量是最为关键的问题。质子交换膜燃料电池(PEMFC)阴极氧还原反应(ORR)的反应速率缓慢,而直接甲醇燃料电池阳极Pt催化剂甲醇氧化(MOR)活性低且易CO中毒。因此,提高Pt的利用率、降低Pt的使用量,研制新型高性能、低成本的Pt催化剂对推动低温燃料电池的发展具有重要意义。为降低Pt的用量,人们主要通过Pt与过渡金属M(M=Fe、Co、Cu、Ni等)合金化来制备尺寸小、分布均匀的Pt基合金纳米催化剂来降低成本及提高催化性能。此外,可利用Pt基合金在还原气氛中热处理会发生吸附诱导Pt表面偏析来调控Pt基合金纳米催化剂的表面成分。本文采用乙酰丙酮铂和乙酸钴为前驱体,通过化学热还原的方法,合成出Pt、Co 原子比分别为 3:1、1:1、1:3 的 Pt3Co/C、PtCo/C、PtCo3/C 催化剂,然后将碳载Pt3Co/C、PtCo/C、PtCo3/C催化剂在还原气氛中400℃分别保温2h、4h、6h来调控Pt-Co合金纳米催化剂的表面成分。运用TEM、XRD、XPS等分析手段研究Pt-Co合金纳米粒子的尺寸、形貌、化学组成及化学价态,并用电化学方法测试Pt-Co合金纳米催化剂的催化性能(ORR、MOR活性)。研究结果如下:(1)利用化学热还原法合成出的不同Pt、Co原子比例(3:1、1:1、1:3)的Pt-Co纳米合金催化剂,分散均匀、平均尺寸小于3nm;(2)通过XRD分析碳载Pt-Co合金纳米催化剂,证实Co已溶入Pt的晶格形成Pt-Co合金,表明我们利用化学热还原法,合成出碳载Pt-Co合金纳米催化剂。电化学测试表明,合成出的碳载Pt-Co合金纳米催化剂对ORR和MOR都有较高活性。其中,PtCo3/C的ORR活性最好,而Pt3Co/C的MOR活性最好;(3)在还原气氛中400℃热处理获得的碳载PtCo纳米合金催化剂,经TEM分析表明Pt-Co合金纳米粒子的尺寸基本没有明显长大。ORR活性测试表明,随着保温时间增加,ORR活性明显提高,但保温时间过长会导致ORR活性下降;MOR活性测试表明,随着保温时间增加,MOR活性明显提高,但保温时间过长会导致MOR活性下降,其中保温2h的MOR活性最好,而PtCo3/C是MOR性能最好的催化剂。
[Abstract]:Fuel cells are one of the most focused and respected green clean energy sources. Fuel cells have low operating temperature, high start-up speed, high power density and low environmental pollution. It is regarded as the new generation of green power conversion device. However, due to the scarcity of Pt resources, the cost of Pt-based catalyst is high, which restricts the development and promotion of proton exchange membrane fuel. So that fuel cells can't be commercialized on a large scale. The most important problem is to improve the catalytic performance of the catalyst and reduce the amount of Pt. The reaction rate of PEMFC cathodic oxygen reduction reaction (ORR) is slow. However, the anode Pt catalyst for methanol oxidation of direct methanol fuel cell has low activity and is prone to CO poisoning. Therefore, it is necessary to improve the utilization of Pt, reduce the amount of Pt used, and develop a new type of high performance. Low-cost Pt catalysts are of great significance in promoting the development of low-temperature fuel cells. Uniformly distributed Pt-base alloy nanocatalysts to reduce cost and improve catalytic performance. The surface composition of Pt-base alloy nanocatalysts can be regulated by adsorption-induced Pt surface segregation during heat treatment in reducing atmosphere. In this paper, acetylacetone platinum and cobalt acetate are used as precursors, and the method of chemical thermal reduction is used. The Pt3Co- / PtCo- / CtCo- / PtCo3 / C catalyst with a ratio of 3: 1 / 1: 1: 1: 3 has been synthesized. Then carbon supported Pt3CoP / PtCoP / PtCo3 / C catalyst was kept at 400 鈩，

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