【作者】 钟新仙；

【导师】 陈金华；

【作者基本信息】 湖南大学 ， 应用化学， 2008， 博士

【摘要】 直接醇类燃料电池(DAFC)具有无污染、燃料来源广、能量转化率高、储存和运输方便等优点,在便携式电源、电动机车和野外电站等领域具有广阔的应用前景,对解决当前世界面临的能源短缺和环境污染两大难题具有重要的现实意义。但是,电极电催化剂的低活性及高价格仍是阻碍DAFC商业化发展的关键问题之一。提高催化剂活性、降低贵金属用量是推动DAFC商业化发展的重要途径。本论文主要研究有机化合物(染料、Nafion、脂肪胺、芳胺等)对DAFC电催化剂或载体的改性,通过傅立叶变换红外光谱(FTIR)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线能量散射谱(EDS)、循环伏安法(CV)、电化学阻抗(EIS)、计时-电流法、Tafel极化曲线等分析测试技术,对电催化剂、电极的形貌、结构、物理化学性质等进行了详细研究。本论文的主要研究工作如下:(1)以Nafion-硫堇(Nf-Th)离子对为分散剂和助催化剂,制备了负载于活性炭上的催化剂NfThPt/C。采用电化学方法考察了NfThPt/C催化剂与商业催化剂E-TEK Pt/C、E-TEK PtRu/C对甲醇的电催化氧化性能。结果表明:在相同金属催化剂担载量情况下,甲醇在NfThPt/C/石墨电极上的氧化峰电流密度分别是E-TEK Pt/C/石墨电极、E-TEK PtRu/C/石墨电极上的7.25倍和3.04倍,而且NfThPt/C催化剂具有较好的抗中毒能力和长期循环稳定性。Nf-Th离子对明显提高了催化剂Pt对甲醇的电催化氧化活性。(2)将有机染料中性红(NR)引入阳极催化剂体系,采用CV、EIS和极化曲线方法考察了Pt/NR/石墨电极对甲醇的电催化氧化性能。在相当Pt催化剂沉积量下,Pt/NR/石墨电极上的交换电流密度和比活性(SA)分别是Pt/石墨电极上的1.25倍和1.83倍,而且具有更好的长期循环稳定性。(3)采用化学方法制备了乙二胺接枝改性碳纳米管( ED/CNTs)以及催化剂PtRu/ED/CNTs和Pt/ED/CNTs。FTIR结果表明,ED已成功地接枝到了CNTs表面。TEM结果表明ED/CNTs载体更有利于PtRu和Pt纳米颗粒的分散和细小化。在金属催化剂担载量相同时,PtRu/ED/CNTs和Pt/ED/CNTs催化剂对乙醇的电催化氧化活性高于PtRu/CNTs和Pt/CNTs催化剂,Pt/ED/CNTs催化剂的催化活性甚至高于PtRu/CNTs。ED/CNTs是乙醇氧化电催化剂的良好载体。(4)以导电聚合物聚中性红(PNR)修饰的石墨电极为载体,负载催化剂Pt,并用于酸性介质中乙醇的电催化氧化。Pt/PNR/石墨电极对乙醇的电催化氧化活性优于Pt/石墨电极。当石墨电极在5.0×10?4 M NR + 0.50 M H2SO4溶液中聚合10圈、催化剂Pt沉积量相当时,乙醇在Pt/PNR/石墨电极上电催化氧化的比活性为3478.00 A C-1,是Pt/石墨电极上(1582.74 A C-1)的2.20倍。结果表明,PNR有利于Pt纳米颗粒的固定,PNR与Pt纳米颗粒间的协同效应提高了催化剂Pt对乙醇的电催化氧化活性及长期循环稳定性。(5)在5.0×10?2 M邻苯二胺(oPD) + 0.20 M Na2SO4溶液中,在CNTs修饰的玻碳(GC)电极上电化学聚合邻苯二胺(PoPD),然后电化学沉积Pt纳米颗粒,得到Pt/PoPD/CNTs/GC电极,并用于氧的电催化还原研究。结果表明,Pt纳米颗粒在PoPD/CNTs复合膜上分散性更好且在酸性介质中对氧还原表现出更高的电催化活性。氧还原在Pt/PoPD/CNTs/GC电极上的比活性为524.20 A C-1,是Pt/GC电极上的2.12倍。采用线性扫描伏安法(LSV)在旋转圆盘电极上考察了氧还原在Pt/PoPD/CNTs/GC电极上的动力学行为。结果表明,在空气饱和的0.10 M H2SO4溶液中,氧还原在Pt/PoPD/CNTs/GC电极上以四电子还原方式为主。PoPD/CNTs复合膜提高了催化剂Pt电催化氧还原的活性。(6)制备了N-羟基邻苯二甲酰亚胺(NHPI)-CNTs复合物,并以其为载体负载催化剂Pt纳米颗粒,用于氧的电催化还原。结果表明氧在Pt/NHPI-CNTs/GC电极上的还原峰电流密度是Pt/GC电极上的1.64倍。动力学研究表明,氧在Pt/NHPI-CNTs/GC电极上的还原主要以四电子方式进行。更多还原

【Abstract】 Direct alcohol fuel cell (DAFC) possesses the wide application in the portable equipment, electric car and field power etc., due to the free (or low)-pollution, abundant sources, high energy efficiency, the easy storage and transportation of the fuel. However, the low electrochemical activity and high cost of electrocatalysts are still one of the key issues hindering the commercial application of DAFC. Therefore, to improve the electrocatalytic activity and to decrease the loading mass of noble metals are effective routes to the commercial application of DAFC. In this dissertation, organic material (such as dye, Nafion, fatty amine, aromatic amine) modified electrocatalysts or catalyst supports in DAFC have been evaluated. Their micrographs, structure, properties and applications have been investigated by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), cyclic voltammetry (CV), chronoamperometry and polarization method, etc. The main points of this dissertation are summarized as follows:(1) Nafion (Nf) - thionine (Th) ion-pair as dispersant and second catalyst was introduced into the preparation of Pt catalyst for methanol electrooxidation and the resulted catalyst supported on carbon (NfThPt/C) was investigated by electrochemical methods. For the same loading mass of catalyst, the peak current density of methanol oxidation on the NfThPt/C/graphite electrode is about 7.25 and 3.04 times as high as that on the E-TEK Pt/C/graphite and E-TEK PtRu/C/graphite electrodes, respectively. Moreover, NfThPt/C catalyst shows excellent anti-poisoning ability and long-term cycle stability. The electrocatalytic properties of Pt for methanol electrooxidation are improved obviously by Nf-Th ion-pair.(2) Organic dye neutral red (NR) was introduced in the anodic electrocatalyst system for methanol oxidation and the resulting electrode was investigated by CV, EIS and polarization method. For the same loading mass of Pt catalyst, 1.25 times larger exchange current density, 1.83 times higher specific activity and better long-term cycle stability can be obtained at Pt/NR/graphite electrode, as compared with the electrode without NR.(3) As the support of Pt and PtRu catalysts for ethanol electrooxidation, the ethylene diamine (ED)-grafted carbon nanotubes (CNTs) were prepared by chemical synthesis method and characterized by FTIR. The morphology and elemental composition of the PtRu/ED/CNTs and Pt/ED/CNTs catalysts were characterized by TEM and EDS, respectively. TEM results demonstrate that the ED-grafted CNTs are beneficial to loading PtRu and Pt electrocatalysts with well dispersion and small particle size. On the other hand, the electrocatalytic properties of the PtRu/ED/CNTs and Pt/ED/CNTs catalysts were characterized by CV and chronoamperometry. Under the same loading mass of catalyst, the electrocatalytic activities of both PtRu/CNTs/graphite and Pt/CNTs/graphite electrodes are enhanced obviously by the introduction of ED. The electrocatalytic activity of the Pt/ED/CNTs/graphite electrode is even higher than that of the PtRu/CNTs/graphite electrode. These results indicate that the ED/CNTs are the promising catalyst support for ethanol electrooxidation.(4) The conductive polymer poly(neutral red) polymerized on the graphite electrode (PNR/graphite) was used as the catalyst support for catalytic oxidation of ethanol in acidic solution and investigated by electrochemical methods. The Pt nanoparticles loaded on the surface of the PNR/graphite electrode exhibit higher electrocatalytic activity for ethanol oxidation in comparison with the Pt supported on the graphite electrode. With the equivalent loading mass of Pt catalyst, the specific activity (SA) at peak a of the Pt/PNR/graphite electrode where PNR was polymerized for 10 cycles in 5.0×10?4 M NR + 0.50 M H2SO4 solution is 3478.00 A C-1 and about 2.20 times as high as that of the Pt/graphite electrode (1582.74 A C-1). The corresponding results imply that the electrochemical performance (high electrocatalytic activity, better long-term cycle stability) of Pt catalyst for ethanol oxidation is improved by the assistance of PNR, which may enhance the immobilization of Pt nanoparticles and reduce the COads poisoning on the Pt surface.(5) Poly(ο-phenylenediamine)/carbon nanotubes (PoPD/CNTs) composite film has been prepared and investigated as the support of Pt nanoparticle electrocatalysts for the oxygen reduction reaction (ORR). The results from SEM and CV indicate that Pt nanoparticles have been highly dispersed on the PoPD/CNTs composite film and exhibit improved electrocatalytic activity for ORR in acid medium. The specific electrocatalytic activity (SA) of the Pt/PoPD/CNTs loaded on the glass carbon (GC) rotating disk electrode (Pt/PoPD/CNTs/GC electrode), in which PoPD was polymerized in 5.0×10?2 Mο-phenylenediamine (oPD) + 0.20 M Na2SO4 solution at pH 1, is 524.20 A C-1 and about 2.12 times higher than that of the Pt/GC electrode. The kinetic behavior of ORR on the Pt/PoPD/CNTs/GC electrode was also investigated by linear sweep voltammetry (LSV). The results indicate that a 4e-reduction of O2 is dominant on the Pt/PoPD/CNTs/GC electrode in air-saturated 0.10 M H2SO4. Additionally, the electrocatalytic performance of Pt catalyst for ORR is improved obviously by the PoPD/CNTs composite film.(6) N-hydroxyphthalimide-carbon nanotubes (NHPI-CNTs) composite as the catalyst support was introduced and the electrocatalytic properties of the Pt/NHPI-CNTs/GC electrode toward the dioxygen reduction reaction (ORR) have been investigated by CV and LSV. From CV, the peak current density of ORR on the Pt/NHPI-CNTs/GC electrode is about 1.64 times higher than that on the Pt/GC electrode. The kinetic parameters demonstrate that a 4e-reduction of O2 to H2O is dominant on the Pt/NHPI-CNTs/GC electrode during the ORR process.更多还原