以铁离子为氧化剂的燃料电池及其钯基阳极催化剂的研究

发布时间：2018-06-25 11:41

本文选题：铁离子 + 燃料电池　；参考：《湖南科技大学》2017年硕士论文

【摘要】：直接醇燃料电池(DAFC)或直接甲酸燃料电池(DFAFC)是一类绿色环保、高能量密度和能量转换密度高的新型电池,近年来受到了广泛的关注。这些电池的阴极使用氧气(或空气)作为氧化剂发生还原,即氧还原反应(ORR)。然而,即使使用目前催化效果最好的Pt和Pt基催化剂,ORR仍然是一个非常缓慢的过程。这降低了电池的放电性能,同时提高了电池的成本。尽管在ORR催化剂方面已经进行了很多优秀的工作,但是提高燃料电池性能的关键性问题仍然亟待解决。因此,寻找其他的氧化剂替代氧气(或空气)具有非常重大的意义。Fe~(3+)是另一个可替代的氧化剂,它具有原料来源广泛、稳定性高和氧化还原电位(E0(Fe~(3+)/Fe~(2+))=0.771V vs SHE)较高等诸多特点。Fe~(3+)在一些常见的催化剂存在下就能很容易地被还原为Fe~(2+),这是因为Fe~(3+)/Fe~(2+)具有较高的交换电流密度,Fe~(3+)/Fe~(2+)电对之间的转换属于可逆的电化学过程。碳、石墨、铂等已经被证实是Fe~(3+)/Fe~(2+)之间氧化还原反应的高效催化剂。另外,对燃料高效氧化是保证燃料电池稳定工作的关键点之一。在碱性条件下,Pd和Pd基催化剂已被证明对醇(或甲酸)氧化具有较好的电催化性能,目前,Pd及其Pd基催化剂对醇(甲酸)氧化都已经做了相当多的研究,包括Pd Au、Pd Ni、Pd Sn等,这些催化剂的金属颗粒分散性很好,并且具有优异的电催化性能。在本论文的研究中,制备了新颖的钯基电催化剂,研究了它们的电催化性能;将它们应用于以Fe~(3+)为氧化剂的新型燃料电池,研究了电池的放电性能。(1)采用化学还原法,以β-环糊精(β-cd)修饰的碳纳米管(b-cd-CNT或者β-cd-C)为载体,在乙二醇溶液中负载Pd或者Pd Sn纳米颗粒,制备Pd Sn/b-cd-CNT,Pd Sn/CNT,Pd/b-cd-CNT,Pd/CNT和Pd/b-cd-C催化剂。通过TEM和XRD对催化剂进行表征,采用循环伏安和计时电流等方法对催化剂的电化学性能进行测试,在碱性条件下,分别测试了这些催化剂对C1-C3醇氧化的性能。结果表明:Pd Sn/b-cd-CNT催化剂对甲醇、乙醇、正丙醇和异丙醇的氧化都有非常强的电催化性能,峰电流密度分别为94、145、184和87 m A?cm-2。(2)采用包覆法制备不同Fe_3O_4含量的Fe_3O_4-C载体,然后利用化学还原法制备Fe_3O_4-C负载的Pd Sn纳米催化剂(Pd Sn/Fe_3O_4-C)。采用透射电镜(TEM)和X射线衍射(XRD)技术对Pd Sn纳米催化剂颗粒的物理性能进行表征;采用循环伏安法(CV)、计时电流法(CA)和交流阻抗(EIS)技术研究了催化剂在碱性条件下对乙醇氧化的电催化活性。结果表明,Pd Sn纳米金属颗粒在Fe_3O_4-C载体上具有较好的分散性.在所制备的催化剂(Pd Sn/Fe_3O_4(2%)-C、Pd Sn/Fe_3O_4(5%)-C、Pd Sn/Fe_3O_4(10%)-C)中、Pd Sn/Fe_3O_4(5%)-C催化剂对乙醇氧化表现出较高的电催化活性,乙醇氧化的峰电流密度达到147m A cm-2,并且Fe_3O_4的加入提高了催化剂的电化学稳定性。相比于Pd/C,Pd Sn/Fe_3O_4(5%)-C对乙醇氧化反应的电荷转移阻力也有大幅度下降。(3)以铁离子为氧化剂取代氧气,制备了新型醇燃料电池。测试了不同阳极催化剂Pd Sn/Fe_3O_4(5%)-C、Pd Sn/b-cd-CNT,Pd Sn/CNT、Pd/b-cd-CNT、Pd/CNT、Pd/b-cd-C和商业Pd/C在不同醇溶液中的放电性能,包括甲醇、乙醇、正丙醇和异丙醇。阴极反应为铁离子在碳粉电极上进行还原。阳极液(醇+1 mol L-1Na OH)和阴极液(Fe~(3+)+0.5 mol L-1Na Cl)之间通过Nafion 117膜隔开。结果表明:以Pd Sn/b-cd-CNT为阳极催化剂时,开路电压在1.14~1.22 V,在甲醇、乙醇、正丙醇和异丙醇中放电功率密度分别为15.2、16.1、19.9和12.2 m W?cm-2。以Pd Sn/Fe_3O_4(5%)-C为阳极催化剂,乙醇为燃料时,开路电压为1.20 V,放电功率密度为18.0 m W?cm-2。(4)以甲酸为燃料、Fe~(3+)为氧化剂组成了一种新型的甲酸/铁离子燃料电池。阳极催化剂为多壁碳纳米管(MWCNT)以及β-环糊精(β-CD)修饰的MWCNT(β-CD-MWCNT)负载的金属钯/锡纳米颗粒:Pd/MWCNT、Pd Sn/MWCNT、Pd/β-CD-MWCNT和Pd Sn/β-CD-MWCNT。运用循环伏安(CV)和计时电流(CA)等技术,研究了它们在碱性条件下对甲酸氧化反应的电催化活性。结果表明,加入适量的金属锡能促进钯对甲酸的电催化氧化,甲酸氧化电位提前,电流密度增加,环糊精的改性对催化剂电催化活性有一定提升。将上述催化剂制成电池阳极片,碳粉制成电极阴极片,组成甲酸/铁离子燃料电池并测试其放电性能。电池的开路电压在0.98~1.2 V之间;以Pd Sn/β-CD-MWCNT为阳极时,其最大放电电流密度达50 m A?cm-2,最大功率密度达12.6 m W?cm-2,远远优于以Pd/C为阳极的电池性能。
[Abstract]:Direct alcohol fuel cell (DAFC) or direct formic acid fuel cell (DFAFC) is a new type of green, high energy density and high energy conversion density, which has been widely paid attention in recent years. The cathode of these batteries is reduced by oxygen (or air) as oxidant, that is, oxygen reduction reaction (ORR). However, even using current catalysis The best Pt and Pt based catalysts, ORR is still a very slow process. This reduces the discharge performance of the battery and increases the cost of the battery. Although many excellent work has been done on the ORR catalyst, the key questions to improve the performance of the fuel cell are still to be solved. The substitute of oxygen (or air) is of great significance..Fe~ (3+) is an alternative oxidant. It has a wide range of raw materials, high stability, and redox potential (E0 (Fe~ (3+) /Fe~ (2+)) =0.771V vs SHE) and a good many characteristics.Fe~ (3+) can be easily reduced to a number of common catalysts. Because Fe~ (3+) /Fe~ (2+) has high exchange current density, the conversion between Fe~ (3+) /Fe~ (2+) electric pairs is a reversible electrochemical process. Carbon, graphite, platinum, etc. have been proved to be efficient catalysts for the redox reaction between Fe~ (3+) /Fe~ (2+). In addition, the efficient oxidation of fuel is one of the key points to ensure the stability of fuel cells. Under alkaline conditions, Pd and Pd based catalysts have been proved to have good electrocatalytic properties for alcohols (or formic acid) oxidation. At present, Pd and its Pd based catalysts have done quite a lot of research on alcohols (formic acid) oxidation, including Pd Au, Pd Ni, Pd Sn and so on. These catalysts have good dispersibility of metal particles and have excellent electrocatalytic properties. In this study, a novel palladium based electrocatalyst was prepared and their electrocatalytic properties were studied. They were applied to a new type of fuel cell with Fe~ (3+) as oxidant. (1) the chemical reduction method was used to use the carbon nanotubes (b-cd-CNT or beta -cd-C) modified by beta cyclodextrin (beta -cd) as the carrier, in B two. Pd or Pd Sn nanoparticles were loaded in the alcohol solution to prepare Pd Sn/b-cd-CNT, Pd Sn/CNT, Pd/b-cd-CNT, Pd/CNT and Pd/b-cd-C catalysts. The catalysts were characterized by TEM and XRD. The electrochemical properties of the catalysts were tested by cyclic voltammetry and chronoampere, and the catalysts were tested under alkaline conditions. The performance of alcohol oxidation shows that Pd Sn/b-cd-CNT catalysts have very strong electrocatalytic properties for methanol, ethanol, propanol and isopropanol. Peak current density is 94145184 and 87 m A? Cm-2. (2), respectively, to prepare Fe_3O_4-C carrier with different Fe_3O_4 content by coating method, and then use chemical reduction method to prepare P of Fe_3O_4-C load. D Sn nano catalyst (Pd Sn/Fe_3O_4-C). The physical properties of Pd Sn nano catalyst particles were characterized by transmission electron microscopy (TEM) and X ray diffraction (XRD). The electrocatalytic activity of the catalyst on the oxidation of ethanol under alkaline conditions was studied by cyclic voltammetry (CV), chronoamperometric (CA) and AC impedance (EIS) technology. D Sn nanoparticles have good dispersibility on Fe_3O_4-C carriers. In the prepared catalysts (Pd Sn/Fe_3O_4 (2%) -C, Pd Sn/Fe_3O_4 (5%) -C, Pd Sn/Fe_3O_4 (10%) -C), the catalysts exhibit higher electrocatalytic activity for ethanol oxidation. The electrochemical stability of the catalyst was improved. Compared to Pd/C, the charge transfer resistance of Pd Sn/Fe_3O_4 (5%) -C to ethanol oxidation was also greatly reduced. (3) a new alcohol fuel cell was prepared by replacing oxygen with iron ions as an oxidant. The different anode catalysts, Pd Sn/Fe_3O_4 (5%) -C, Pd Sn/b-cd-CNT, Pd Sn/CNT, Pd/b-cd-CN, were tested. The discharge performance of T, Pd/CNT, Pd/b-cd-C and commercial Pd/C in different alcohol solutions, including methanol, ethanol, n-propanol and isopropanol. The reaction of the cathode to the reduction of the iron ions on the carbon electrode. The anode solution (alcohol +1 mol L-1Na OH) and the cathode liquid (Fe~ (3+) +0.5 mol) are separated by the 117 membrane. When the anode catalyst is used, the open circuit voltage is at 1.14~1.22 V, the discharge power density in methanol, ethanol, propanol and isopropanol is 15.2,16.1,19.9 and 12.2 m W? Cm-2. with Pd Sn/Fe_3O_4 (5%) -C as the anode catalyst. When ethanol is used as fuel, the open circuit voltage is 1.20 V and the discharge power density is 18 m W? 4 with formic acid as the fuel. A new type of formic acid / iron ion fuel cell is formed. The anode catalyst is the metal palladium / tin nanoparticles loaded with multi wall carbon nanotubes (MWCNT) and beta cyclodextrin (beta -CD) modified MWCNT (beta -CD-MWCNT): Pd/MWCNT, Pd Sn/MWCNT, Pd/ beta -CD-MWCNT and Pd Sn/ beta -CD-MWCNT. using cyclic voltammetry and timing current. The results show that the electrocatalytic oxidation of palladium to formic acid can be promoted by adding a proper amount of metal tin, the oxidation potential of formic acid is ahead of time, the current density increases, the modification of cyclodextrin has a certain increase in the electrocatalytic activity of the catalyst. The catalyst is made into a battery anode and carbon powder. The electrode cathode is made to form a formic acid / iron ion fuel cell and test its discharge performance. The open circuit voltage of the battery is between 0.98~1.2 V; the maximum discharge current density of Pd Sn/ beta -CD-MWCNT is 50 m A cm-2, the maximum power density reaches 12.6 m W? Cm-2, far superior to the battery performance with Pd/C as the anode.
【学位授予单位】：湖南科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36;TM911.4

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