氧还原非铂催化剂的研究

发布时间：2018-06-24 04:27

本文选题：燃料电池 + 氧还原　；参考：《重庆大学》2014年博士论文

【摘要】：质子交换膜燃料电池（PEMFC）具有高效和洁净等突出优点，是最有发展前途的一种动力电池，可广泛用于移动电源和便携式电源。目前，PEMFCs主要催化剂为贵金属Pt类催化剂。然而，Pt储量低、价格高等问题严重阻碍了PEMFCs的商业化进程。开发高效低成本的非铂催化剂替代Pt类催化剂催化氧还原反应（ORR）是成功实现燃料电池商业化的关键。近年来，非铂催化剂的ORR催化活性已有大幅提高，但仍与Pt基催化剂有很大差距。如何提高非铂催化剂在大电流工况下的催化活性已成为非Pt催化剂实际应用的关键。基于此，探究非金属催化剂的活性中心、开发提高活性位密度的先进制备技术、构筑高效非铂催化电极结构是当前非铂催化剂研究的主要方向。本文开展了如下几方面的研究工作：（1）开发高活性高稳定的Pd类催化剂。Pd的催化性质与Pt类似，而其储量是Pt的50倍，价格为Pt的1/3，被认为是替代Pt催化剂降低成本的最优选择之一。然而，相比Pt催化剂Pd催化剂的氧还原催化活性低，稳定性差。本文第三章中，开展基于金属/氧化物载体界面价键调控钯电子结构增强活性和稳定性的研究：研究通过单片层蒙脱土载体（ex-MMT）调控Pd的表面电子结构，使其d带中心更趋近与Pt，降低其氧中间物种吸附能，获得了一种催化活性与Pt类似、稳定性优异的Pd/ex-MMT催化剂。研究发现，界面共价氧化物的形成，是活性稳定性增强的主要原因。该研究为优化Pd表面电子结构、提高Pd催化活性稳定性提出了一种新方法。在燃料电池中应用该催化剂，可降低20%燃料电池的成本。（2）探究非金属氮掺杂碳阴极催化剂的氮键合结构与活性的关系，开发选择性掺氮技术。氮掺杂石墨烯具有比表面积高、导电性高等特点。但是，其制备过程复杂、活性位点不明、酸性介质中活性差，使其难于作为ORR催化剂商业化应用。本文第四章中，开展空间限制-诱导合成平面吡啶吡咯氮掺杂的石墨烯以及其氧还原催化性能的研究：开发了一种简单易行成本低廉的方法制备石墨烯，即通过扁平纳米反应器制备氮掺杂石墨烯。具有平面结构的吡啶吡喏氮（Planar N）以p电子参与石墨烯π共轭体系，，有助于与之相邻的碳原子活化和石墨烯导电性的提高。季氨氮则由于其键角影响，形成三维立体结构破坏石墨烯局部π共轭体系，从而影响导电性。本研究通过调节纳米反应器的宽度，可选择性的合成具有平面结构的吡啶氮和吡喏氮掺杂的石墨烯。通过不同平面氮含量的氮掺杂石墨烯，构建平面氮—导电性—催化活性之间的构效关系。其中，ORR活性最高的氮掺杂石墨烯平面氮含量高达93%，其催化氧还原半波电位与商业化Pt/C催化剂仅相差60mV，单电池测试的最大功率可达340mW·cm-2。该方法所制备的石墨烯具有良好的导电性和酸性条件下优异的ORR催化活性。（3）开发高利用率高活性位点密度的PEMFC阴极电极。构建高效氧还原催化电极，除引入更多活性位点外，活性位点的暴露同样非常重要。本文第五章中，开展了基于形态控制转换纳米聚合物制备高效氧还原碳纳米材料催化剂的研究：研究通过氯化钠重结晶方法以固定前驱聚合物的纳米形态，通过热解，获得具有优异孔结构、表面性质的催化剂。该催化剂保持原前驱物的几何形貌和孔结构。氯化钠晶体为催化剂石墨化和氮掺杂提供全封闭的反应空间。优异的三维传输通道、高度石墨化的碳结构以及活性氮掺杂的表面性质，极大增加了暴露在催化三相界面的活性位点数量。以该催化剂制备的阴极电极，其最高功率达600mV·cm-2，与Pt/C催化剂的ORR活性处于同一个数量级。开发的此类新型材料已经具备了在燃料电池发动机中完全替代Pt/C催化剂的可能性。
[Abstract]:Proton exchange membrane fuel cell (PEMFC) has the outstanding advantages of high efficiency and cleanliness. It is one of the most promising power batteries, which can be widely used in mobile and portable power sources. At present, the main catalyst of PEMFCs is Pt catalyst of precious metals. However, the low Pt reserves and high price have seriously hindered the commercialization of PEMFCs. The key to commercialization of fuel cells is the high efficiency and low cost non platinum catalyst instead of Pt catalyst (ORR). In recent years, the ORR catalytic activity of non platinum catalysts has been greatly improved, but there is still a big gap with the Pt based catalyst. How to improve the catalytic activity of the non platinum catalyst in the high current condition has become a great problem. The key to the practical application of non Pt catalysts is to explore the active center of non-metallic catalysts, to develop advanced preparation techniques for increasing the density of active sites, and to construct a high efficiency non platinum catalytic electrode structure is the main direction of the current research on non platinum catalysts.
This article has carried out the following aspects of research work:
(1) the catalytic properties of the highly active and highly stable Pd catalyst.Pd are similar to that of Pt, and their reserves are 50 times of Pt and the price is Pt, which is considered to be one of the best alternatives for reducing the cost of the Pt catalyst. However, the catalytic activity of the Pt catalyst Pd catalyst is low and the stability is poor. In this third chapter, metal / oxygen is carried out in the third chapter. Study on the regulation of the enhanced activity and stability of the palladium electronic structure by the interface valence bond of the material carrier: the study of the surface electronic structure of Pd by single layer montmorillonite (ex-MMT), which makes the center of the D closer to and Pt, reduces the adsorption energy in the intermediate oxygen species, and has obtained a kind of Pd/ex-MMT catalyst, which has a similar catalytic activity with Pt and has excellent stability. It is found that the formation of covalent oxide at the interface is the main reason for the enhancement of the activity stability. A new method is proposed to optimize the electronic structure of the Pd surface and improve the stability of the catalytic activity of Pd. The application of the catalyst in fuel cells can reduce the cost of 20% fuel cells.
(2) to explore the relationship between nitrogen bonding structure and activity of non-metallic nitrogen doped carbon cathode catalyst and the development of selective nitrogen doping technology. Nitrogen doped graphene has high specific surface area and high conductivity. However, the preparation process is complex, the active site is unknown, and the activity of acid medium is poor, so it is difficult to be used as the commercial application of ORR catalyst. In the fourth chapter, space restriction - induced synthesis of planar pyridine pyrrole - doped graphene and its catalytic performance in oxygen reduction are studied. A simple and inexpensive method is developed to prepare graphene, that is, the preparation of nitrogen doped graphene through a flat nano reactor. The planar structure of pyridine pyridine nitrogen (Planar N) with P electricity The participation of the son in the graphene pi conjugation system is helpful to the activation of the adjacent carbon atoms and the increase of the conductivity of graphene. The quaternary ammonium nitrogen, because of its bond angle, forms a three-dimensional structure that destroys the local pi conjugation system of graphene, thus affecting the conductivity. The structure-activity relationship between planar nitrogen doping and catalytic activity was constructed by different planar nitrogen content of nitrogen doped graphene. Among them, the nitrogen content of nitrogen doped graphene with the highest ORR activity was up to 93%, and the catalytic oxygen reduction half wave potential was only 60mV with commercial Pt/C catalyst. The maximum power of the single cell test can reach 340mW. Cm-2.. The graphene prepared by this method has good conductivity and excellent ORR catalytic activity under acidic conditions.
(3) developing a PEMFC cathode electrode with high active site density and high active site density. Construction of a high performance oxygen reduction catalytic electrode is also very important. In addition to the introduction of more active sites, the exposure of active sites is also very important. In the fifth chapter, a study on the preparation of high effect oxygen reduction carbon nanomaterials based on morphologic control conversion nanoparticles was carried out. The nano morphology of precursor polymers was immobilized by sodium chloride recrystallization. By pyrolysis, a catalyst with excellent pore structure and surface properties was obtained. The catalyst maintains the geometric morphology and pore structure of the precursor. The NaCl crystal provides a completely closed reaction space for the catalyst graphitization and nitrogen doping. The highly graphitized carbon structure and the surface properties doped by active nitrogen greatly increase the number of active sites exposed to the catalytic three-phase interface. The cathode electrode prepared by this catalyst has the highest power of 600mV. Cm-2, and the ORR activity of the Pt/C catalyst is in the same number of orders. The possibility of completely replacing Pt/C catalyst in fuel cell engine.
【学位授予单位】：重庆大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：O643.36;TM911.4

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