碳材料上多元催化剂的负载与催化性能研究

发布时间：2018-06-15 09:44

本文选题：甲醇氧化反应 + 氧还原反应　；参考：《武汉工程大学》2015年硕士论文

【摘要】：目前直接甲醇燃料电池(DMFC)的研究虽然取得了很大的进展,但其商业化的目标依然难以实现,其主要原因是一些关键技术并未得到有效的解决。从技术层面上来讲,DMFC的发展仍然受到催化剂活性低、催化剂及整体DMFC成本高的限制。因此,研究催化活性高、成本低的催化剂对DMFC实现商业化具有重要的意义。本论文采用微波辅助多元醇还原法制备了低成本的PtxAgy/CNTs、PtAgxCoy/CNTs、AgxCoy/CNTs催化剂,通过材料表征手段和多种电化学研究方法着重研究了催化剂的形貌、晶体结构、电化学活性等。取得如下研究成果:1)XRD结果表明实验制备的三种催化剂均有合金相的出现。酸性介质中,PtxAgy/CNTs催化剂的甲醇氧化活性随着合金化程度的增大而有所提高,其中PtAg3/CNTs催化剂的电化学活性表面积(ECSA)最大,为134.4 m2/g。甲醇氧化实验结果表明PtAg3/CNTs催化剂的活性及稳定性相对最好,其甲醇氧化峰电流密度为32.1 mA.mg-1。在碱性介质中,催化剂中Ag的氧化物含量显著地影响着PtxAgy/CNTs催化剂的甲醇氧化活性。2)PtAgxCoy/CNTs催化剂的活性均比PtxAgy/CNTs催化剂的活性高。酸性介质中,PtAgxCoy/CNTs催化剂的电化学活性表面积(ECSA)普遍比较大,其中PtAg3Co/CNTs催化剂的ECSA最大,为272.7 m2/g,相同条件下,商业Pt/C催化剂的ECSA为266.6 m2/g。甲醇氧化实验结果表明除了PtAgCo5/CNTs外其他样品的甲醇氧化电流都要比商业Pt/C的大,其中PtAg3Co/CNTs显示出了最好的甲醇氧化催化活性,氧化峰电流密度达到了191.3 mA.mg-1,这要比商业Pt/C的峰电流密度值(84.2 mA.mg-1)高出两倍多。此外,Tafel斜率曲线结果证实了PtAgxCoy/CNTs催化剂的吸附机制基本都与商业Pt/C催化剂相一致。3)AgxCoy/CNTs催化剂不具备甲醇氧化活性。本论文采用循环伏安法(CV)、旋转圆盘电极(RDE)、计时电流(CA)等电化学研究方法重点研究了AgxCoy/CNTs催化剂的氧还原反应(ORR)催化活性、反应动力学参数、稳定性等。该系列催化剂的ORR活性受活化电位的影响很大。根据Koutecky-Levich曲线得出不同催化剂上ORR的电子转移数介于3.1与4.0之间,其中商业Pt/C催化剂的电子转移数为3.8。此外,计时电流测试结果表明,NH3改性能够显著地提高催化剂的稳定性。
[Abstract]:Although great progress has been made in the research of direct methanol fuel cell (DMFC), the goal of its commercialization is still difficult to achieve. The main reason is that some key technologies have not been solved effectively. Technically speaking, the development of DMFC is still limited by the low activity of catalyst and the high cost of catalyst and DMFC as a whole. Therefore, it is of great significance to study the catalysts with high catalytic activity and low cost for the commercialization of DMFC. In this paper, the low cost PtxAgy- CNTs-PtAgxCoy- CNTs-AgxCoy- CNTs catalyst was prepared by microwave-assisted polyol reduction method. The morphology, crystal structure and electrochemical activity of the catalyst were studied by means of material characterization and various electrochemical methods. The following results were obtained: (1) XRD results showed that alloy phase appeared in the three kinds of catalysts. The methanol oxidation activity of PtAg3 / CNTs catalyst increased with the increase of alloying degree in acid medium, and the electrochemical activity surface area of PtAg3 / CNTs catalyst was the largest (134.4 m2 / g). The results of methanol oxidation test showed that PtAg3 / CNTs catalyst had the best activity and stability, and the peak current density of methanol oxidation was 32.1 mA.mg-1. In alkaline medium, the oxide content of Ag in the catalyst significantly affected the methanol oxidation activity of PtxAg / CNTs catalyst. The activity of PtAgxCoy / CNTs catalyst was higher than that of PtxAgyxCoy / CNTs catalyst. The electrochemical activity surface area of PtAgxCoy / CNTs catalyst is generally larger than that of PtAg3Co-CNTs catalyst in acidic medium, and the ECSA of PtAg3Co/ CNTs catalyst is the largest (272.7 m2 / g). Under the same conditions, the ECSA of commercial PtAgxCoy / CNTs catalyst is 266.6 m2 / g. The results of methanol oxidation test showed that the methanol oxidation current of other samples except PtAgCo5 / CNTs was higher than that of commercial Pt / C. among them, PtAg3Co/ CNTs showed the best catalytic activity for methanol oxidation. The oxidation peak current density is 191.3 mA.mg-1, which is more than twice the peak current density of commercial PT / C (84.2 mA.mg-1). In addition, the Tafel slope curve shows that the adsorption mechanism of PtAgxCoy / CNTs catalyst is basically consistent with that of commercial Pt / C catalyst. 3AgxCoy / CNTs catalyst has no methanol oxidation activity. In this paper, the catalytic activity, kinetic parameters and stability of AgxCoy / CNTs catalyst for oxygen reduction reaction were studied by cyclic voltammetry (CV), rotating disk electrode (RDE) and chronoelectric current (CAA). The ORR activity of this series of catalysts is greatly affected by the activation potential. According to Koutecky-Levich curve, the electron transfer number of ORR on different catalysts was found to be between 3.1 and 4.0, and the electron transfer number of commercial PT / C catalyst was 3.8. In addition, the results of chronoamperometric measurement show that NH _ 3 modification can significantly improve the stability of the catalyst.
【学位授予单位】：武汉工程大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：O643.36;TM911.4

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