过渡金属氧化物氧还原催化机理的第一性原理研究

发布时间：2018-07-09 22:14

本文选题：质子交换膜燃料电池 + 第一性原理　；参考：《武汉理工大学》2014年博士论文

【摘要】：质子交换膜燃料电池是一种通过电化学反应将化学能直接转化为电能的电化学装置。由于具备高能量效率、高功率密度、室温快速启动和污染物零排放等优点，它被看作是未来移动和固定电源的理想能量来源。但是，燃料电池的商业化发展受到了催化剂成本和催化活性的严重阻碍。因此，低成本和高催化活性的新型催化剂研究是燃料电池发展的关键。由于良好抗强酸腐蚀性能，低成本阀金属氧化物在质子交换膜燃料电池催化剂研究中备受关注。本论文采用第一性原理方法，以ZrO2基催化剂为研究对象，系统研究了过渡金属氧化物氧还原催化机理和氮掺杂过渡金属氧化物氧还原催化活性增强机理。在第一性原理计算基础上，构建了过渡金属氧化物催化剂中的催化活性中心原子的d-band电子填充度与催化剂的氧还原催化活性关系，并提出了一种适用于过渡金属氧化物氧还原催化剂的新催化活性指示符(d-band电子填充度)。基于提出的催化活性指示符，设计出新的过渡金属氧化物氧还原催化剂。具体研究进展如下： (1)采用第一性原理方法，系统研究了单斜ZrO2晶面对氧还原催化过程的影响。研究发现，O原子在不同单斜ZrO2晶面吸附时，都会受到表面Zr原子的“空间位阻效应”影响，且在不同单斜ZrO2晶面O2分子都通过“联合机制”还原为H2O分子。研究还发现，O2分子吸附速率对单斜ZrO2(-111)和(-101)晶面的氧还原反应速率起决定性作用，而单斜ZrO2(110)晶面的氧还原反应速率则由OOH*形成速率决定。 (2)采用第一性原理方法，系统研究了不同晶相ZrO2表面的氧还原催化过程。研究发现，对于不同晶相ZrO2表面而言，，所有的Zr原子催化活性中心都存在“空间位阻效应”，然而O原子趋于在“空间位阻效应”较弱的Zr原子表面吸附。研究还发现，在不同晶相ZrO2表面，O2分子都通过“联合机制”还原生成H2O分子。单斜和立方ZrO2表面的氧还原反应速率由O2分子吸附速率决定，然而四方ZrO2表面的氧还原反应速率则由OOH*解离速率决定。 (3)采用第一性原理方法，系统研究了氮掺杂ZrO2的氧还原催化活性增强机理。研究发现，氮掺杂处理可以将O2分子吸附方式从单斜ZrO2表面的端式吸附转变为氮掺杂ZrO2表面的侧式吸附，从而促进O2分子在氮掺杂ZrO2表面通过“解离机制”还原生成H2O分子。研究还发现，OH*脱吸附速率对氮掺杂ZrO2表面的氧还原反应速率起决定性作用，而单斜ZrO2表面的氧还原反应速率则由OOH*形成速率决定。 (4)采用第一性原理方法，研究了上述三章所涉及平板模型的电子态密度分布。研究发现，平板模型中表面Zr原子d-band电子填充度与其表面的氧还原反应活性成正比例关系，即表面氧还原催化活性随表面Zr原子填充度的增加而增强。基于此，我们提出将过渡金属氧化物氧还原反应催化剂中催化活性中心原子的d-band电子填充度作为这类催化剂的催化活性指示符。 (5)在第四章基础上，采用溶胶-凝胶法和改性Adams法制备了不同形貌的IrO2催化剂。研究发现，溶胶-凝胶法制备的IrO2催化剂具有棒状结构，而改性Adams法合成的IrO2催化剂具有椭球粒状结构。在酸性电解质中，当电极电势低于0.3V或高于1.3V时，棒状IrO2催化剂表面表现出显著的阴极析氢和阳极析氧特征。在电极电势介于0.3~1.3V范围内，棒状IrO2催化剂表面的电化学特征为典型的赝电容特征。棒状IrO2/C催化剂的电化学稳定性显著高于商业Pt/C催化剂。在碱性电解质中，椭球粒状IrO2的氧还原催化活性高于棒状IrO2催化剂。高过电势下，两种IrO2催化剂的氧还原路径以四电子转移为主，而低过电势下，两种IrO2催化剂的氧还原路径以两电子转移为主。
[Abstract]:Proton exchange membrane fuel cell (PEMFC) is an electrochemical device that converts chemical energy directly into electrical energy by electrochemical reaction. Due to its advantages of high energy efficiency, high power density, rapid starting at room temperature and zero discharge of pollutants, it is considered as an ideal source of energy for future mobile and fixed power sources. However, the commercialization of fuel cells Development is seriously hindered by the cost and catalytic activity of the catalyst. Therefore, the research of new catalysts with low cost and high catalytic activity is the key to the development of fuel cells. Due to the good corrosion resistance of strong acid, low cost valve metal oxide has attracted much attention in the research of proton exchange membrane fuel cell catalyst. On the basis of the first principle calculation, the d-band electron filling degree of the catalytic active center atom in the transition metal oxide catalyst is constructed on the basis of the first principle calculation. The mechanism of oxygen reduction catalysis and the catalytic activity enhancement mechanism of the nitrogen doped transition metal oxide oxide reduction catalysis are systematically studied with the ZrO2 based catalyst as the research object. The relationship between the catalytic activity of oxygen reduction catalyst and a new catalytic activity indicator (d-band electron filling degree) suitable for the transition metal oxide oxygen reduction catalyst were proposed. Based on the proposed catalytic activity indicator, a new transition metal oxide oxygen reduction catalyst was designed. The specific research progress is as follows:
(1) the effect of monoclinic ZrO2 crystal on the catalytic process of oxygen reduction is systematically studied by the first principle method. It is found that O atoms are affected by the "space hindrance effect" of the surface Zr atoms when adsorbed on different monoclinic ZrO2 crystal surfaces, and the O2 molecules of different monoclinic ZrO2 planes are reduced to H2O molecules by "joint mechanism". It is also found that the adsorption rate of O2 molecules plays a decisive role in the rate of oxygen reduction reaction of monoclinic ZrO2 (-111) and (-101) crystal, while the rate of oxygen reduction reaction of monoclinic ZrO2 (110) crystal is determined by the formation rate of OOH*.
(2) the catalytic process of oxygen reduction on the surface of different crystalline phase ZrO2 is systematically studied by the first principle method. It is found that, for different crystalline phase ZrO2 surfaces, all the Zr atomic catalytic active centers have "space hindrance effect", while O atoms tend to adsorb on the surface of the "space hindrance effect" on the surface of the Zr atoms. Now, on the surface of different crystalline phase ZrO2, the O2 molecules are reduced to H2O molecules by "joint mechanism". The rate of oxygen reduction reaction on the surface of monoclinic and cubic ZrO2 is determined by the adsorption rate of O2 molecules. However, the rate of oxygen reduction reaction on the surface of tetragonal ZrO2 is determined by the dissociation rate of OOH*.
(3) using the first principle method, the mechanism of oxygen reduction catalytic activity enhancement of nitrogen doped ZrO2 is systematically studied. It is found that nitrogen doping can change the end adsorption of O2 molecular adsorption from the surface of monoclinic ZrO2 to the side adsorption on the surface of nitrogen doped ZrO2, thus promoting the O2 molecule to pass the "dissociation mechanism" on the surface of nitrogen doped ZrO2. It is also found that the rate of deadsorption of OH* plays a decisive role in the rate of oxygen reduction reaction on the surface of ZrO2 doped ZrO2, while the rate of oxygen reduction reaction on the monoclinic ZrO2 surface is determined by the formation rate of OOH*.
(4) using the first principle method, the electronic density distribution of the plate model in the above three chapters is studied. It is found that the surface Zr atom d-band electron filling degree is proportional to the oxygen reduction reaction activity on the surface, that is, the surface oxygen reduction catalytic activity is enhanced with the increase of the surface Zr atom filling degree. In this case, we propose the d-band electron filling degree that catalyzes the active center atom in the catalyst of the transition metal oxide oxygen reduction reaction as an indicator of the catalytic activity of this type of catalyst.
(5) on the basis of the fourth chapter, the IrO2 catalysts with different morphologies were prepared by the sol-gel method and the modified Adams method. It was found that the IrO2 catalyst prepared by the sol-gel method had a rod like structure, and the IrO2 catalyst synthesized by the modified Adams method had ellipsoidal granular structure. In the acid electrolyte, the electrode potential was lower than 0.3V or higher than 1.3V. The surface of the rod like IrO2 catalyst shows significant cathodic hydrogen evolution and anodic oxygen evolution characteristics. The electrochemical characteristics of the rod like IrO2 catalyst are typical pseudopotential characteristics in the range of 0.3~1.3V in the electrode potential. The electrochemical stability of the rod like IrO2/C catalyst is significantly higher than the commercial Pt/ C catalyst. In the alkaline electrolyte, the ellipsoid granular IrO is in the alkaline electrolyte. The oxygen reduction catalytic activity of 2 is higher than that of the rod like IrO2 catalyst. Under the potential, the oxygen reduction path of the two IrO2 catalysts is four electron transfer, while the oxygen reduction path of the two IrO2 catalysts is dominated by two electron transfer under the low potential.
【学位授予单位】：武汉理工大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM911.4;O643.31

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