Knowledge Management System Of Institute of process engineering,CAS
|关键词||氧还原反应 催化剂 中性 碱性 多金属氧酸盐 碳材料|
当今社会，由化石能源过度消耗引起的能源危机、环境污染问题日益突出，制约着社会的进步、危害人们的身体健康。因此，开发新型绿色能源技术已是迫在眉睫。燃料电池可以通过正负极的氧化还原反应将储存在化学物质中的化学能直接转化为电能，产物只有水。这种能量转换技术转换效率高、绿色环保、构造简单、稳定性好、启动快，近些年掀起了研究热潮，成为继化石能源后又一重要的能源利用形式。然而，燃料电池内部阴极的氧气还原反应(ORR)动力学过程比阳极反应慢，大大降低了电池的输出电压。为提高阴极反应速率，常用的传统催化剂为铂(Pt)。但是铂价格昂贵，稳定性差，严重制约了燃料电池的大规模商业化发展。因此研发廉价、高效的燃料电池阴极ORR催化剂是推动燃料电池发展产业的重要研究课题之一。本论文主要通过掺杂碳材料和复合多金属氧酸盐(多酸，POMs)两种方法制备非Pt的非贵金属和无金属的ORR催化剂，并研究了材料在不同pH条件下催化氧还原的性能。取得以下研究成果：(1) 通过对石墨炔进行杂原子掺杂处理，研发了一种新型、无金属、掺杂石墨炔的二维碳材料。对石墨炔进行N、B、 S、 F单原子和NS、NB、NF双原子的掺杂，制备了掺杂材料，并在碱性条件下分别对其进行半电池和全电池性能测试，发现NF共掺的材料的半电池及全电池测试性能均优于其它材料。并且材料在稳定性、抗甲醇干扰性、抗CO中毒性能等方面都优于Pt/C。密度泛函理论(DFT)计算从机理角度解释了掺杂效应。实验表明掺杂石墨炔是一种廉价、稳定、高效的非金属催化剂。 (2) 开发了一种自下而上设计合成催化剂的方法。以对二氰基苯为单体，在实验指导下自下而上的通过不同反应温度、不同反应时长及不同元素掺杂处理等条件制备结构可控的三维多孔碳材料(PTF)，并进行电化学测试以研究该材料在碱性条件下的催化ORR性能。发现，随着温度升高，材料的导电性大幅度提升，催化效果显著；N的形态对材料催化ORR影响显著，石墨氮是活性最高的N形态；不同元素影响氧还原反应不同的反应参数：B有利于提高材料的选择性，F有利于提高起始电位和电流密度。通过这种自下而上的制备方法为氧还原反应机理的研究带来便利。在此工作的基础上还探索了通过引入Fe和I，制备适用于酸性介质中的ORR催化剂。发现Fe和I的掺杂顺序对材料性能影响明显，先掺Fe后掺I的PTF-Fe-I性能最好。(3) 首次制备一种多金属氧酸盐和碳材料复合的非贵金属多酸基复合材料，并用于催化中性和碱性条件下的氧还原反应。借助多酸和碳材料强相互作用力，简单一步法制备了复合材料。将该材料用于中性及碱性介质中测试，发现材料出现4e-催化反应区，研究了多酸基催化剂催化ORR的反应机理。该工作对于指导多酸在燃料电池中的应用提供了借鉴意义。(4) 开发了一种将含有不同3 d金属的多酸和不同的碳基底材料复合的简单方法。将制备的材料用于中性及碱性条件氧还原催化，研究了不同的3 d金属(Cu，Co，Ni)和不同的碳基底材料(Vulcan XC-72，石墨烯，有机碳材料)对材料性能的影响。探索制备高效多酸基复合催化剂的多酸活性位点和优秀的碳材料的条件。
Recently, the rising global energy crisis and environmental impact of traditional fossil fuels pose serious challenges to human health and social development. Develop novel green energy technologies are badly in need. Fuel cell can directly generate electricity from chemical energy stored in materials by electrochemically redoxing reactions in anode and cathode with water as the only byproduct. This energy conversion technology currently receives intensive development focus and becomes another important energy technology after fossil energy because of its high energy conversion efficiency, virtually no pollution, simple structure, significant stability and easy starting. However, the oxygen reduction reaction (ORR) in the cathode is much more kineticly sluggish than the reaction in anode, which restricts the efficiency and performance of such devices. Traditionally, platimum (Pt) has been commonly used as the best ORR catalyst. Unfortunately, its high cost and instability in the fuel cell environment have also made Pt-based catalysts the primary barrier to commercial mass market of fuel cells. Thus, efforts are needed to identify alternative catalysts that are readily available, cost effective, and show comparable-or even better-catalytic effects than Pt for cathodic in fuel cells.Herein, a series of none Pt catalysts are prepared by doping carbon materials and combine polyoxometalates with different carbon materials used as ORR catalysts in different electrolyte. The main results are as follows:(1) A novel kind of highly efficient metal-free electrocatalysts for ORR has been developed successfully by doping heteroatoms in graphdiyne. Mono-element (N, B, F, S) and dual elements (NS, NB, NF) are introduced in the graphdiyne, leading to series dopant graphdiyne. In particular, the as-prepared NFGD exhibits comparable performance to commercial Pt/C both in half-cell and full-cell (Zn–air battery). It shows a much better stability as well as a higher tolerance to methanol crossover and CO poisoning effects than the commercial Pt/C. The density functional theory (DFT) calculations give proper explaination to the doping effect. Our results show that these doped GDs have great potential for metal-free catalysts to be used as low-cost, effcient, and durable ORR catalysts.(2) Develop a new strategy to prepare catalysts by bottom-up synthesis route. The metal-free catalysts were prepared using a nitrogen containing molecule, terephthalonitrile, as the precursor through different thermal temperature, reaction time and elements doping to get the 3D porous structure material (PTF). On this novel platform, we observe that the nitrogen confgurations can greatly influence the electrocatalytic performances of the catalysts, and quaternary nitrogen (Niii) can be the most effecient nitrogen configuration for ORR. In addition, different heteroatoms have disparate influences to the parameters of ORR catalysts: boron doping can improve the catalytic selectivity, while fluorine doping can enhance the catalytic activity. Obviously, the rational design of catalysts via bottom-up strategies developed in this work opens up a new avenue for detailed exploration of the electrochemical mechanisms of metal-free catalysts. Based on the work, we also explored the catalyst used in acid medium by introduced Fe and I to the organic framework. The results showed that the doping sequence of Fe and I has great influence on the catalytic activity of the as prepared cataysts. And the best catalyst is PTF-Fe-I, which introduced Fe firstly, then I.(3) A novel cathode catalyst made of the noble metal free polyoxometalate (POM) Co7(AlePyZn)2 and low cost carbon materials Vulcan XC-72 is highly active toward the ORR in both neutral and basic media. Owning to the strong electrostatic interaction between POM and carbon, the composite were obtained through one step.The as prepared materials reduced O2 to H2O in both neutal and basic media in a 4e- parthway and the reaction mechanism of POM-based materials used as ORR catalysts was studies. This work opened up a new avenue for the application of POM in electrochemical catalytic field.(4) A new and simple approach for the fabrication of noble metal-free ORR electrocatalysts based on 3d-substituted POMs and carbonaceous materials was developed. The POM-based materials were used as the ORR catalysts in both basic and neutal medium, which presented a good platform to shed light on the influence of different 3d metals (Cu, Co, Ni) and carbon support (Vulcan XC-72, rGO, organic carbon materials) on the catalytic activities. This approach also paves the way for the development of a whole new family of efficient active sites of POM and excellent carbon supports.
|张双双. 非铂类高效氧还原催化剂的设计及性能研究[D]. 北京. 中国科学院研究生院,2017.|