直接甲醇质子交换膜燃料电池阳极催化剂研究

为了提高直接甲醇质子交换膜燃料电池阳极催化剂的活性和降低毒化现象，本论文选择并且通过电化学阴极还原一阳极氧化的方法制备了铂修饰的氧化钦电极和铂、钉共修饰的氧化钦电极两种修饰电极，对于甲醇在两种修饰电极上的电催化氧化行为进行了研究；通过化学还原和溶胶一凝胶两步骤法制备了碳载Pt-TiO_2和碳载Pt-Ru-TiO_2复合催化剂，运用测定极化曲线和放电寿命的方法考察了催化剂对于甲醇的电催化氧化活性，研究了热处理条件对催化剂性能的影响佩研究了改变催化剂的组成对性能的影响．通过XPS, XRD，TEM等技术对催化剂性能改进的原因进行了分析，并且对催化剂作用的机理进行了合理的推导．初步研究了几种催化剂对CO的电催化氧化。并得到如下结果： 1.用电化学方法制备的Pt-TiO_x/Ti、Pt-Ru-TM/Ti电极对甲醇的氧化呈现了很好的电催化活性，比相应的Pt和Pt-Ru电极的活性要高出很多。Pt-Ru-Ti电极对甲醇的电催化高于Pt-TiO_x/Ti电极。其中TiO_x是TiO_2和TiO(OH)的混合物，甲醇在Pt-TiO_x/Ti电极和Pt-Ru-TiOX_/Ti电极上氧化的最终产物是CO_2。 Pt-TiO_X/Ti电极对甲醇的氧化呈现了很好的电催化活性的原因之一是Pt和TiO_x粒子之间的很好分散。由于Pt和TiO_x粒子的相互作用，甲醇氧化的中间产物如CO在电极表面的吸附能力大大降低，因此，降低了电极被甲醇氧化的中间产物毒化的可能性，这是Pt-TiO_x/Ti电极对甲醇的氧化呈现了很好的电催化活性的重要原因。由于Pt, Ru, TiO、之间的协同作用，Pt-Ru-TiO_x／Ti电极对甲醇的氧化呈现了比Pt-TiO_x/Ti电极更高的电催化活性。但由于在较高的过电位下，Ru易生成氧化物，并易在酸性溶液中溶解，因此，Pt-Ru-TiO_x／Ti电极最宜在中性溶液中使用修饰电极表面的修饰层由分散度很高的Pt和TiO_x粒子或Pt、Ru和TiO_x粒子组成，高的催化活性是各物种之间协同作用的结果。由于Pt和Ti0：粒子以及Pt, Ru和Ti0：粒子的相互作用，甲醇氧化的中间产物如CO在电极表面的吸附能力大大降低，因此，降低了电极被甲醇氧化的中间产物毒化的可能性。2.通过化学还原和溶胶一凝胶法制备的Pt-TiO_2/C催化剂对甲醇的电催化氧化呈现出了很好的活性和稳定性。这主要是由于Pt和TiO_x之间的协同作用使甲醇氧化的中间产物中的毒化物种易氧化成最终产物的结果。其次是用这种方法制得的Pt-TiO_2/C催化剂中各组分具有较小粒径，并能很好相互分散。另外，催化剂中的Ti和Pt的原子比也有很大的影响，当Ti和Pt的原子比为1/2时，所得的催化剂的性能最好。这是由于合适的Ti和Pt的原子比使Pt和TiO_x产生最佳的协同作用，另外Ti0：的导电性较差要求Pt有较多的含量。在500℃下热处理后，催化剂的性能得到进一步的改善，这是由于热处理使催化剂中Pt金属的含量增加，而R氧化物的含量降低引起的。这种催化剂有望能在DMPEMFC实际使用。用同样方法制备的Pt-Ru-TiO_2/C催化剂对甲醇的电催化氧化呈现出了比Pt-TiO_2/C催化剂更高的活性，但性能提高的不是很多，这主要是由于催化剂中的Ru及其氧化物所起到的作用与TiO_x相似，在催化剂中氧化物的比例较高时，降低了电极的导电性的缘故．Pt-Ru-TiO_2/C催化剂的稳定性不如Pt-TiO_2/C催化剂好，这主要是因为Ru金属及其氧化物在酸性介质中容易溶解，造成这些物种在催化剂中减少，影响到催化剂的性能．3.对于CO电催化氧化研究的结果表明，用电化学阴极还原一阳极氧化法制得的Pt-TiO_x/Ti修饰电极与P七电极相比，对CO氧化的峰电位发生负移，具有更高的催化活性；与Pt/C催化剂相比，由于TiO_x的存在，Pt-TiO_2/C催化剂对于CO氧化的活性得到了提高。

Highly active PtRu catalysts supported on carbon nanotubes prepared by modified impregnation method for methanol electro-oxidation

A simple and rapid synthesis method (denoted as modified impregnation method, MI) for PtRu/CNTs (MI) and PtRu/C (MI) was presented. PtRu/CNTs (MI) and PtRu/C (MI) catalysts were characterized by transmission electron microscopy (TEM) and X-ray diffractometry. It was shown that Pt-Ru particles with small average size (2.7 nm) were uniformly dispersed on carbon supports (carbon nanotubes and carbon black) and displayed the characteristic diffraction peaks of Pt face-centered cubic structure.

WO3/C hybrid material as a highly active catalyst support for formic acid electrooxidation

The hybrid material based on WO3 and Vulcan XC-72R carbon has been used as the support of Pd nano-catalysts. The resultant Pd-WO3/C catalysts in a large range of WO3 content exhibit excellent catalytic activity and stability for formic acid electrooxidation. The great improvement in the catalytic performance is attributed to the uniform dispersion of Pd with less particle sizes on the WO3/C support and the hydrogen spillover effect which greatly accelerates the dehydrogenation of HCOOH on Pd.

High activity PtRu/C catalysts synthesized by a modified impregnation method for methanol electro-oxidation

A modified impregnation method was used to prepare highly dispersive carbon-supported PtRu catalyst (PtRu/C). Two modifications to the conventional impregnation method were performed: one was to precipitate the precursors ((NH4)(2)PtCl6 and Ru(OH)(3)) on the carbon support before metal reduction: the other was to add a buffer into the synthetic solution to stabilize the pH. The prepared catalyst showed a much higher activity for methanol electro-oxidation than a catalyst prepared by the conventional impregnation method. even higher than that of current commercially available, state-of-the-art catalysts. The morphology of the prepared catalyst was characterized using TEM and XRD measurements to determine particle sizes, alloying degree, and lattice parameters. Electrochemical methods were also used to ascertain the electrochemical active surface area and the specific activity of the catalyst.

三氧杂环己烷的电化学特性

直接氧化一些有机小分子(如甲醇[1~9]和乙醇[10~14]等)的直接氧化燃料电池作为一种对环境友好的能源越来越引起人们的关注.三氧杂环己烷作为一种可再生的能源,可以从地球上存在的大量天然气中得到,来源广泛,价格低廉.三氧杂环己烷反应的基本结构如Scheme 1所示,相对乙醇而言,三氧杂环己烷不存在任何碳碳键,反应更易进行.目前广泛研究的直接氧化燃料电池均采用液体甲醇和S chem e 1 S tru ctu re of tr ioxane乙醇等作燃料,液体燃料的存储运输存在一定的安全隐患,一旦泄漏发生危险,后果非常严重,而三氧杂环己烷作为一种固体,可以有效地避免上述问题的发生,利于安全的储存和运输.Narayanan等[13]研究了三氧杂环己烷在Pt,Pt-Sn和Pt-Ru电极上的电化学行为及其在燃料电池中的应用.本文研究了三氧杂环己烷在不同浓度、不同温度和不同酸度时于光滑铂电极上的电化学行为,初步分析了三氧杂环己烷的反应机理.1实验部分1.1试剂与仪器采用Potentiostat/GalvanostatModel 273A恒电位仪(美国Princeton Applied Research公司),在传统的三...

一种新型直接甲醇燃料电池阳极添加剂的电化学研究

将磷钼酸 (H4PMo12 O40 ·xH2 O ,PMo12 )作为一种添加剂 ,制备了直接甲醇燃料电池阳极Pt Ru/C PMo12 复合催化剂 ,并对甲醇在含有此复合催化剂的阳极上的氧化进行了电化学研究 .测试表明该添加剂降低了甲醇及其电氧化中间产物转化的活化能 ,改善了电极内部的质子传输状况 ,对甲醇的电化学氧化过程具有明显的促进作用 ,该复合催化剂与常规的Pt Ru/C催化剂相比 ,甲醇的阳极氧化电流提高了 46% .添加剂的这一效应可能与磷钼酸的Keggin结构有关

Physical and electrochemical characterizations of PtRu/C catalysts by spray pyrolysis for electrocatalytic oxidation of methanol

In this paper, it was reported that the carbon-supported Pt-Ru(Pt-Ru/C) catalyst used as the anodic catalyst in the direct methanol fuel cell (DMFC) was synthesized with a two-step spray pyrolysis (SP) method using the Pt and Ru metal salt as the precursors and polyethylene glycol (PEG) with the different molecular weights (Mw= 200,600,and 1000 analytical reagent) as cosolvent. PEG as a cosolvent plays a crucial role in producing PtRu/C catalysts. It was found that the Mw of PEG could affect the electrocatalytic activity of Pt-Ru and the morphology of the Pt-Ru particles in the Pt-Ru/C catalysts prepared with this method. When the Mw of PEG is 600, the Pt-Ru particles in the Pt-Ru/C catalyst prepared with this method possess the small average size, narrow size distribution, uniform dispersion, and high electrochemically active specific surface area. The electrocatalytic activity of the Pt-Ru/C catalyst prepared with this method using the cosolvent PEG with Mw = 600 for the methanol oxidation is much higher than that of the commercial E-TEK Pt-Ru/C catalyst. Therefore, the two-step SP method is an excellent method for the preparation of the Pt-Ru/C catalyst used in DMFCs.

碳纳米管负载铂催化剂的制备及其对甲醇的电催化氧化研究

Pt金属是直接甲醇燃料电池(DMFC)常用的催化剂犤1～3犦。为了尽可能减少Pt金属用量,提高Pt的分散度,人们总是选择具有高表面积的基质,如石墨、碳黑、活性碳、分子筛、质子交换膜等,作为Pt金属的载体犤3～5犦。最初,人们以为载体的作用仅仅是提供表面积和多孔气体扩散电极的骨架,使Pt微粒可以有更大的比表面积与反应物接触,但是现在普遍认为犤1犦,当Pt金属负载在活性炭上时,它们中的催化性能有一部分应归结于金属和载体之间的相互作用,因此,载体的形貌及物理化学性质直接影响着催化剂对甲醇的电催化氧化活性。碳纳米管(CNTs)由于其拥有纳米级管腔结构、较高的比表面积、类石墨的多层管壁等特点,使它在做催化剂载体方面有着良好的应用前景犤6～9犦。CheGuangli等人犤6犦在探索CNTs的潜在用途时,曾研究了将Pt、Ru、PtRu等金属或合金沉积在CNTs的内壁,并讨论了其在DMFC上的潜在用途。本文通过液相化学还原的方法制得Pt载量为20%的Pt/CNTs催化剂,并研究了预处理对催化剂形貌、表面基团及其对甲醇电催化氧化性能的影响。1实验部分1.1试剂和仪器实验所用试剂均为分析纯,所有溶液均用三次蒸馏水配制。

铂、钌共修饰的氧化钛电极对甲醇的电催化氧化

首次发现用电化学阴极还原 -阳极氧化法制得的 Pt-Ti Ox/Ti和 Pt-Ru-Ti Ox/Ti电极对甲醇氧化呈现出较高的电催化活性和稳定性 ,其中 Pt-Ru-Ti Ox/Ti电极比 Pt-Ti Ox/Ti电极具有更好的性能 .实验结果表明 ,这两种电极对甲醇氧化具有高电催化活性是由于 Pt、Ru得到了较好的分散 ,较好的稳定性可归结于Pt、Ru与 Ti Ox 协同作用导致弱的 CO吸附而使电极不易中毒 .

滇西菲红超基性岩风化壳铂族元素地球化学行为

近年来在世界不同地区进行了风化过程中铂族元素的地球化学行为研究。作为中国西南部的第一个实例． 本文研究了云南西部菲红超基性岩体上发育的红土化风化剖面。矿物学和微量元素地球化学研究证明该风化壳 是超基性岩风化的结果。文中详细讨论了风化壳的地质、矿物学、红土化和铂族元素地球化学特征。结果表明， 风化壳的红土化程度不高，仍处于红色牯土阶段；风化壳上酃的表层土壤带和铁质牯土带中铂族元素总量至少富 集了3 57—7．盯倍，其中Ru和Pd的富集程度较大，Ix的富集程度中等，Pt和弛的富集程度较小，使得铂族元素 的配分模式由基岩的Pt富集型转变为风化壳的Ru-Pt富集型，证明红土化过程中铂族元素发生了分异。

Determination of ionic resistance and optimal composition in the anodic catalyst layers of DMFC using AC impedance

In the present study, a method based on transmission-line mode for a porous electrode was used to measure the ionic resistance of the anode catalyst layer under in situ fuel cell operation condition. The influence of Nafion content and catalyst loading in the anode catalyst layer on the methanol electro-oxidation and direct methanol fuel cell (DMFC) performance based on unsupported Pt-Ru black was investigated by using the AC impedance method. The optimal Nafion content was found to be 15 wt% at 75 degrees C. The optimal Pt-Ru loading is related to the operating temperature, for example, about 2.0 mg/cm(2) for 75-90 degrees C, 3.0 mg/cm2 for 50 degrees C. Over these values, the cell performance decreased due to the increases in ohmic and mass transfer resistances. It was found that the peak power density obtained was 217 mW/cm(2) with optimal catalyst and Nafion loading at 75 degrees C using oxygen. (c) 2005 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

Pt nanoparticles: Heat treatment-based preparation and Ru(bpy)(3)(2+)-mediated formation of aggregates that can form stable films on bare solid electrode surfaces for solid-state electrochemiluminescence detection

A simple thermal process for the preparation of small Pt nanoparticles is presented, carried out by heating a H-2-PtCl6/3- thiophenemalonic acid aqueous solution. The following treatment of such colloidal Pt solution with Ru( bpy)(3)(2+) causes the assembly of Pt nanoparticles into aggregates. Most importantly, directly placing such aggregates on bare solid electrode surfaces can produce very stable films exhibiting excellent electrochemiluminescence behaviors.

Pt based anode catalysts for direct ethanol fuel cells

In the present work several Pt-based anode catalysts supported on carbon XC-72R were prepared with a novel method and characterized by means of XRD, TEM and XPS analysis. It was found that all these catalysts are consisted of uniform nanosized particles with sharp distribution and Pt lattice parameter decreases with the addition of Ru or Pd and increases with the addition of Sn or W. Cyclic voltammetry (CV) measurements and single direct ethanol fuel cell (DEFC) tests jointly showed that the presence of Sn, Ru and W enhances the activity of Pt towards ethanol electro-oxidation in the following order: Pt1Sn1/C > Pt1Ru1/C > Pt1W1/C > Pt1Pd1/C > Pt/C. Moreover, Pt1Ru1/C further modified by W and Mo showed improved ethanol electro-oxidation activity, but its DEFC performance was found to be inferior to that measured for Pt1Sn1/C. Under this respect, several PtSn/C catalysts with different Pt/Sn atomic ratio were also identically prepared and characterized and their direct ethanol fuel cell performances were evaluated. It was found that the single direct ethanol fuel cell having Pt1Sn1/C or Pt3Sn2/C or Pt2Sn1/C as anode catalyst showed better performances than those with Pt3Sn1/C or Pt4Sn1/C. It was also found that the latter two cells exhibited higher performances than the single cell using Pt1Ru1/C, which is exclusively used in PEMFC as anode catalyst for both methanol electro-oxidation and CO-tolerance. This distinct difference in DEFC performance between the catalysts examined here would be attributed to the so-called bifunctional mechanism and to the electronic interaction between Pt and additives. It is thought that an amount of -OHads, an amount of surface Pt active sites and the conductivity effect of PtSn/C catalysts would determine the activity of PtSn/C with different Pt/Sn ratios. At lower temperature values or at low current density regions where the electro-oxidation of ethanol is considered not so fast and its chemisorption is not the rate-determining step, the Pt3Sn2/C seems to be more suitable for the direct ethanol fuel cell. At 75 degreesC, the single ethanol fuel cell with Pt3Sn2/C as anode catalyst showed a comparable performance to that with Pt2Sn1/C, but at higher temperature of 90 degreesC, the latter presented much better performance. It is thought from a practical point of view that Pt2Sn1/C, supplying sufficient -OHads and having adequate active Pt sites and acceptable ohmic effect, could be the appropriate anode catalyst for DEFC. (C) 2003 Elsevier B.V. All rights reserved.