碳基钼化合物复合载体的制备及对Pt催化剂性能影响研究

发布时间：2018-06-20 19:59

本文选题：直接甲醇燃料电池 + 担载型Pt催化剂　；参考：《哈尔滨工业大学》2017年博士论文

【摘要】：随着能源危机、环境污染等问题的日趋严重,绿色能源的开发与应用逐渐走入大众的视野。直接甲醇燃料电池(DMFC)以其能量密度高、储存安全、操作方便、启动速度快等特点,有望大规模应用在电动汽车、移动电源等领域。想要取得商品化的应用,需满足电池性能好、循环寿命长、生产成本低等条件。Pt基催化剂是DMFC阳极的核心部分,催化剂活性和稳定性的高低直接影响DMFC的性能。本文主要从合成低廉、高效、稳定的碳基钼化合物复合载体方面开展基础研究工作,以得到催化活性高、稳定性好且持久耐用的Pt基催化剂。开发了一步水热法合成的氮掺杂碳量子点与碳纳米管(NCQDs-MWCNT)、氮掺杂碳量子点与石墨烯(NCQDs-GN)复合载体提高催化剂活性的新方法,详细研究了Pt基催化剂的性能。研究发现:NCQDs在高温水热下与MWCNT、GN紧密结合,形成碳复合载体;NCQDs表面的含氧基团增强了复合载体在溶液中的亲水性,为Pt粒子的沉积提供更多的活性位点;小粒径NCQDs的存在,使Pt粒子同时沉积在NCQDs与MWCNT的交界面上,有利于Pt粒子的分散。Pt/NCQDs-MWCNT、Pt/NCQDs-GN催化剂分别与Pt/MWCNT、Pt/GN相比,都表现出了更高的甲醇氧化活性。同时,考察了前驱体添加量对Pt/MWCNT催化剂性能的影响,随着前驱体添加量的增加,NCQDs在MWCNT上的团聚导致含氧官能团的减少,进而使催化剂性能下降。综合考虑Pt催化剂表现出的不同性能,得到最佳前驱体添加量。为进一步提高催化剂的活性和稳定性,采用氧化钼(Mo O_2、Mo O_3)与碳复合作为Pt基催化剂的载体,研究了烧结温度对载体结构、和对催化剂性能影响的规律。通过模板自组装法合成多层的碳包覆Mo O_2纳米管核壳结构复合载体,实现了Mo O_2与碳的均匀结合。该特殊纳米管核壳结构,不仅具有大的比表面积,而且存在Mo O_2核与碳层之间的相互作用,有利于Pt纳米粒子的沉积以及增加碳上的固Pt位。结果表明:当烧结温度为800 o C时,催化剂Pt/Mo O_2@C表现出最优的甲醇氧化活性以及稳定性。若烧结温度过低时,载体表面碳化不完全,不利于Pt的沉积。若烧结温度过高,晶体物相发生改变,使碳层无序化程度增加,造成载体结构的不稳定。与Pt/Mo O_2@C催化剂相比,采用高温烧结法合成的Mo O_3-C新型碳复合载体对应的Pt催化剂,具有更高的甲醇氧化活性和稳定性。催化剂性能提高的原因是Mo O_3可以为碳表面提供大量的含氧官能团,有利于Pt粒子的沉积与分散。同时,MoO_3有助于吸附CO等反应中间体转化成CO_2,提高载体的耐腐蚀性。结果表明:烧结温度为850 o C时,催化剂Pt/Mo O_3-C的甲醇氧化活性是商业Pt/C的1.95倍,稳定性是商业Pt/C的2.36倍。在保证催化剂活性的前提下,为进一步提高催化剂的稳定性、耐久性以及降低其生产成本,设计了化学性质稳定的二硫化钼(MoS_2)与碳材料复合,考察了不同MoS_2添加量对Pt催化剂性能的影响。采用水热法构筑了多层结构的MoS_2-GN纳米片。层状的MoS_2-GN复合材料提供更多的电荷传递通道,有效促进了电荷的传递。MoS_2好的耐腐蚀性,且多层载体结构有利于固定Pt纳米粒子,可以很大程度上提高催化剂的稳定性。当添加量为15%时,催化剂Pt/MoS_2-GN的催化活性和稳定性表现最好。相比于Pt/GN催化剂,Pt/MoS_2-GN的甲醇氧化活性是其1.92倍,稳定性比其提高了26.7%。与Pt/MoS_2-GN催化剂相比,Pt/MoS_2-MWCNT表现出更高的稳定性。其中,当添加量为37.5%时,催化剂的性能表现最优。相比于Pt/MWCNT催化剂,Pt/MoS_2-MWCNT的甲醇氧化活性是其2.0倍,稳定性比其提高了33.2%。催化性能的提高归因于特殊3D结构的设计,具有较高的空隙率以及高效的电荷传输通道。MoS_2可以抑制MWCNT的团聚,提供更多的Pt粒子沉积的活性位点。另外,耐腐蚀性强的MoS2与导电性好的MWCNT复合,增强了载体的导电性和抗腐蚀性,有利于提高催化剂整体的电化学性能。考察了磷化钼(Mo P)与碳材料复合作为载体的可行性,通过微波辅助乙二醇法制备了Pt基催化剂。实验结果表明:Pt/Mo P-GN催化剂的甲醇氧化电流密度是Pt/GN的1.54倍,稳定性比后者提高了17.5%。性能提高的主要原因是:(1)Pt与Mo P之间存在强烈的电子间相互作用;(2)Mo P为还原石墨烯表面提供官能团,有利于Pt纳米粒子的分散;(3)Mo P与GN之间的相互作用,提高了催化剂载体的耐腐蚀性能。
[Abstract]:With the energy crisis, environmental pollution and other problems becoming more and more serious, the development and application of green energy has gradually entered the public view. Direct methanol fuel cell (DMFC) has the characteristics of high energy density, safe storage, convenient operation, fast starting speed and so on. It is expected to be widely used in the fields of electric vehicles, mobile power sources and so on. The.Pt based catalyst is the core part of the DMFC anode, and the activity and stability of the catalyst directly affect the performance of DMFC. This paper mainly studies the basic research work on the synthesis of carbon based molybdenum compound carrier, which is low, efficient and stable. A new Pt based catalyst with high activity, good stability and durable durability has been developed. A new method of hydrothermal synthesis of nitrogen doped carbon quantum dots and carbon nanotubes (NCQDs-MWCNT), nitrogen doped carbon quantum dots and Shi Moxi (NCQDs-GN) composite carrier to improve the activity of the catalyst was developed. The performance of the Pt based catalyst was studied in detail. The study found that NCQDs was in high temperature water. The heat is closely combined with MWCNT and GN to form a carbon composite carrier, and the oxygen bearing group on the NCQDs surface enhances the hydrophilicity of the composite carrier in the solution and provides more active sites for the deposition of Pt particles; the presence of small particle size NCQDs makes Pt particles deposited on the interface of NCQDs and MWCNT at the same time, which is beneficial to the dispersive.Pt/NCQDs-MWCNT and Pt/NCQ of Pt particles. The Ds-GN catalyst showed higher methanol oxidation activity compared with Pt/MWCNT and Pt/GN. At the same time, the effect of the precursor addition on the performance of Pt/MWCNT catalyst was investigated. With the increase of the precursor addition, the aggregation of NCQDs on MWCNT resulted in the reduction of oxygen containing functional groups and reduced the performance of the catalyst. The catalytic performance of the catalyst decreased. The catalytic performance of the catalyst decreased. The catalytic performance of the catalyst was reduced by Pt catalysis. In order to further improve the activity and stability of the catalyst, in order to further improve the activity and stability of the catalyst, using molybdenum oxide (Mo O_2, Mo O_3) and carbon composite as the carrier of the Pt based catalyst, the regularity of the sintering temperature on the carrier structure and the performance of the catalyst was studied. The multilayer carbon package was synthesized by the template self assembly method. The composite carrier of Mo O_2 nanotube core shell structure has realized the uniform combination of Mo O_2 and carbon. The core shell structure of the special nanotube not only has a large specific surface area, but also has the interaction between the Mo O_2 core and the carbon layer, which is beneficial to the deposition of Pt nanoparticles and the increase of the solid Pt position on the carbon. The results show that when the sintering temperature is 800 o C, The catalyst Pt/Mo O_2@C shows the best oxidation activity and stability of methanol. If the sintering temperature is too low, the carbonization of the carrier surface is not perfect, which is not conducive to the deposition of Pt. If the sintering temperature is high, the phase of the crystal is changed, the degree of disordering of the carbon layer is increased and the structure of the carrier is unstable. Compared with the Pt/Mo O_2@C catalyst, the high temperature is adopted. The new carbon composite carrier of Mo O_3-C synthesized by sintering method has higher oxidation activity and stability of methanol. The reason for improving the performance of the catalyst is that Mo O_3 can provide a large number of oxygen containing functional groups on the carbon surface, which is beneficial to the deposition and dispersion of Pt particles. At the same time, MoO_3 helps to convert the intermediate of CO and other reaction intermediates into CO_2, The corrosion resistance of the carrier was improved. The results showed that when the sintering temperature was 850 o C, the methanol oxidation activity of the catalyst Pt/Mo O_3-C was 1.95 times that of the commercial Pt/C, and the stability was 2.36 times of the commercial Pt/C. The chemical properties were designed to further improve the stability, durability and lower production cost of the catalyst, on the premise of ensuring the activity of the catalyst. The stable molybdenum disulfide (MoS_2) was combined with carbon materials, and the effects of different MoS_2 additions on the performance of Pt catalysts were investigated. The multilayer structure of MoS_2-GN nanoscale was constructed by hydrothermal method. The layered MoS_2-GN composites provided more charge transfer channels, which effectively promoted the good corrosion resistance of the charge transfer.MoS_2 and the multi-layer carrier. The structure is beneficial to the immobilization of Pt nanoparticles, which can greatly improve the stability of the catalyst. When the amount of addition is 15%, the catalytic activity and stability of the catalyst Pt/MoS_2-GN is best. Compared with the Pt/GN catalyst, the oxidation activity of methanol is 1.92 times that of the catalyst, and the stability is higher than that of the Pt/MoS_2-GN catalyst, Pt. Pt /MoS_2-MWCNT shows higher stability. Among them, when the amount of addition is 37.5%, the performance of the catalyst is the best. Compared with the Pt/MWCNT catalyst, the oxidation activity of methanol is 2 times that of Pt/MoS_2-MWCNT. The improvement of the stability of the catalyst is attributed to the design of the special 3D structure, with higher void ratio and high efficiency than that of the catalyst. The charge transfer channel.MoS_2 can inhibit the aggregation of MWCNT and provide more active sites for the deposition of Pt particles. In addition, the corrosion resistant MoS2 combined with good conductive MWCNT enhances the conductivity and corrosion resistance of the carrier, and is beneficial to the improvement of the overall electrochemical energy of the catalyst. The composite of molybdenum phosphide (Mo P) and carbon materials is investigated. The Pt based catalyst was prepared by microwave assisted ethylene glycol method. The experimental results show that the methanol oxidation current density of Pt/Mo P-GN catalyst is 1.54 times of Pt/GN, and the main reason for the improvement of 17.5%. performance is: (1) Pt and Mo P exist between strong electron interaction; (2) Mo P is reduced graphite. The functional groups on the surface of the alkene are beneficial to the dispersion of Pt nanoparticles. (3) the interaction between Mo P and GN improves the corrosion resistance of the catalyst carrier.
【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O643.36

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