【作者】 马娟；

【导师】 郑军伟；

【作者基本信息】 苏州大学 ， 物理化学， 2011， 博士

【摘要】 低温燃料电池是一种小型的电源技术,由于其具有操作简单、燃料储存运输方便、适合作为便携设备电源等特点,吸引了越来越多研究者的关注。然而,低温燃料电池中阴极和阳极催化剂低的催化效率及其高昂价格是抑制低温燃料电池商业化的瓶颈之一。因此,如何提高催化剂的活性和稳定性,减少贵金属的载量,有效降低电池的制造成本成为非常有意义的工作。本文围绕这一研究主题,开展了以下几个方面的工作。1.络合-自还原法制备碳载Pt纳米粒子催化剂及其对乙醇的电催化氧化使用乙二胺四甲叉膦酸为络合剂制备Pt^Ⅳ络合物,利用Pt^Ⅳ络合物自还原法制备Vulcan XC-72碳载Pt纳米粒子（Pt/C）催化剂的方法。在制备Pt/C催化剂的过程中,Pt纳米粒子的大小可以通过控制反应溶液的pH有效控制。TEM照片显示,Pt纳米粒子在Vulcan XC-72碳载体上分散性良好,并且具有较小的粒径分布范围。因此,利用这种方法制备的系列Pt/C催化剂非常适合用来研究Pt纳米粒子电催化乙醇氧化的粒径效应。Pt/C催化剂中Pt纳米粒子粒径大小与其催化乙醇电氧化的活性关系研究表明:平均粒径在2.5 nm左右的碳载Pt纳米粒子对乙醇的氧化具有最佳的电催化性能。2.碳载Pt-Sn催化剂的制备及其对乙醇氧化的电催化性能以Pt（NO₃）₂和SnO作前驱体,使用热分解法制备了碳载Pt-Sn纳米粒子（Pt-Sn/C）催化剂。X射线衍射（XRD）、透射电镜（TEM）、X射线光电子能谱（XPS）等表征技术显示该法制备的Pt-Sn/C催化剂中的Pt-Sn纳米粒子具有Pt-Sn合金粒子外壳和SnO_x粒子为核的核壳结构。循环伏安法、CO溶出等电化学方法显示催化剂对乙醇氧化的电催化性能要好于商业化的碳载Pt（Pt/C）催化剂。特别是乙醇在Pt-Sn/C催化剂电极上的循环伏安曲线中,出现了一个少有报道的0.32 V左右的乙醇氧化肩峰。此外,该制备方法没有引入Cl^-,制得的催化剂不需要洗涤,不易引起环境污染。因此,这是一种具有潜在实现的、可规模化工业生产的制备方法。3.碳载Pt-P催化剂的制备及其氧还原电催化性能利用硝酸亚铂（Pt（NO₃）₂）和白磷（P4）制备出了碳载Pt-P纳米粒子（Pt-P/C）催化剂。该方法制备的Pt-P/C催化剂中磷含量较高,Pt-P粒子的粒径随着P4投料量的增加而减小。该方法制备的Pt-P/C催化剂的氧还原催化（ORR）性能优于商业化的Pt/C催化剂。实验结果显示白磷直接还原掺杂法制备Pt-P/C催化剂的方法是一种实践可行的制备方法。磷掺杂后,Pt/C催化剂对氧还原（ORR）电催化性能提高的主要原因是Pt、P之间形成合金,降低了Pt的电子密度。4.均相沉淀-原位还原法制备高分散的Pd/C催化剂利用简单的均相沉淀-原位还原法制备了一种超细、高分散的碳载Pd纳米粒子（Pd/C）催化剂。在特定的pH条件下,由于自身缓慢的水解作用,PdCl₂溶液中可溶性的[PdCl₄]^2-物种会缓慢转化为不可溶的氧化钯水合物（PdO·H₂O）,这导致高分散、小粒径的碳载PdO·H₂O纳米粒子（PdO·H₂O/C）的生成。随后利用NaBH₄还原即可制得高分散、超细的Pd/C催化剂。电化学性能测试显示该种Pd/C催化剂对甲酸的电催化氧化具有很高的活性,这与该种Pd/C催化剂具有较小粒子粒径和高分散性相关。更多还原

【Abstract】 Low temperature fuel cells are attracting increasing interest as a compact power sources for portable applications, mainly due to the relatively simple handling, storage, and transportation of fuel molecules. However, the low electrocatalytic performance of catalyst for target molecules is one of the major challenges in the commercialization of low tempeture fuel cell. Thus, it is important to improve the activity or stability of catalyst, reduce the platinum group metal loading and decrease particle size of platinum group metal catalyst. As these issues to be addressed, the following researches have been carried out.1. Ethanol electrooxidation on carbon-supported Pt catalyst prepared using complexing self-reduction methodA novel self-reduction of Pt-complex method is used to prepare Vulcan XC-72 carbon-supported Pt nanoparticles （Pt/C） catalysts by employing ethylenediamine-tetramethylene phosphonic acid （EDTMP） as complexing reagent. During the preparation of Pt/C catalysts, the particles size of Pt nanoparticles （Pt-NPs） can be controlled effectively by reaction solution pH. TEM images demonstrate that the Pt nanoparticles well disperse on the Vulcan XC-72 carbon support with a relatively narrow particle size distribution by using the complex self-reduction method. Therefore, the Pt/C catalysts prepared by the same method are suitable for evaluating the size effect of the Pt-NPs on electrocatalytic performance for ethanol electrooxidation. A correlation between the electrocatalytic activity of ethanol oxidation and particle size of the Pt/C catalysts indicates that Pt-NPs with mean particle size of 2.5 nm possesse the highest electrocatalytic performance for ethanol electrooxidation.2. Synthesis of carbon supported PtSn catalyst and its elctrocatalytic performance for ethanol oxidationOne kind Pt-Sn/C catalyst had been synthesized firstly by solid phase reacted and then direct thermo-decomposition treatment. It is the first time that stannous oxide was used as the reactor for PtSn/C, and our product almost needn’t any distilled water for our reaction without Cl^-1. In our experiments, an enhancement of the activity for the ethanol oxidation was observed on the binary catalyst. The catalyst was investigated by employing various physicochemical analyses: X-ray diffraction （XRD）, transmission electron microscopy （TEM） and X-photoelectron spectroscopy （XPS）. Cyclic voltammetry （CV） measurements showed that the affiliation of Sn improves the electro-catalytic activities for the oxidation of ethanol. The initial potential of the anodic peak of ethanol at the Pt-Sn/C catalyst electrode with the atomic ratio of Pt and Sn = 1:1 is at -67 mV. This is attributed to that Sn can promote the oxidation of ethanol at Pt through the direct pathway because Sn can decrease the adsorption strength of CO on Pt.3. Preparation of carbon supported Pt-P catalysts and its elctrocatalytic performance for oxygen reductionThe carbon supported PtP （PtP/C） catalysts were synthesized from Pt（NO₃）₂ and phosphorus yellow at the room temperature. The content of P in the PtP/C catalysts prepared with this method is high and the average size of the PtP particles is decreased with increasing the content of P. The electrocatalytic performances of the PtP/C catalysts prepared with this method for the oxygen reduction reaction （ORR） are better than that of the commercial Pt/C catalyst. The promotion action of P for enhancing the electrocatalytic performances of the PtP/C catalyst for ORR is mainly due to that Pt and P form the alloy and then the electron density of Pt is decreased.4. Preparation of highly dispersed carbon supported Pd catalyst by facile homogeneous precipitation-reduction reaction methodA highly dispersed and ultrafine carbon supported Pd nanoparticles （Pd/C） catalyst was synthesized by a facile homogeneous precipitation method. Under the appropriate pH conditions, [PdCl₄]^2- species in PdCl₂ solution can slowly transformed into the insoluble palladium oxide hydrate （PdO·H₂O） precipitation by treatment due to slow hydrolysis reaction, which results in the generation of carbon supported PdO·H₂O nanoparticles （PdO·H₂O/C） sample with the high dispersion and small particle size. Thus, a highly dispersed and ultrafine Pd/C catalyst can be synthesized by PdO·H₂O→Pd⁰ in-situ reduction reaction path in the presence of NaBH₄. As a result, the resulting Pd/C catalyst possessed a significantly electrocatalytic performance for formic acid oxidation, which can be attributed to the uniformly sized and highly dispersed nanostructure, which provided a larger overall electrochemical active surface area.更多还原