锚定增强型直接甲醇燃料电池阳极担载PtRu催化剂研究

发布时间：2018-04-13 06:48

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

【摘要】：由于现代社会化石能源的急剧消耗及由此带来的环境污染问题,直接甲醇燃料电池(DMFC)作为一种绿色能源方案引起众多学者的广泛关注。但是,目前DMFC中的PtRu阳极催化剂的性能仍然不能满足商业化的要求。本论文以“锚定PtRu颗粒”为核心,从“物理包覆锚定”和“化学键合锚定”的方向出发,探索制备了多种高性能的PtRu催化剂,并解释其催化活性和稳定性的提高的原因。详细考察了葡萄糖水热碳化包覆处理对PtRu/C催化剂甲醇催化氧化性能的影响。研究发现:自制PtRu/C催化剂经过葡萄糖碳化锚定处理后,其稳定性提升一倍。这一方面是由于在PtRu纳米合金粒子周围包覆了一层更加稳定的碳层,抑制了金属粒子在载体表面迁移团聚;另一方面则是由于经过水热处理后纳米金属粒子的合金化程度增强。另外,水热碳化处理后催化剂表面会形成大量有助于增强催化剂抗毒化能力的含氧基团,使催化剂在金属颗粒粒径长大的负面影响下保持较好的初始催化活性。当水热处理时间为4 h,包覆碳量为9%时,催化剂表现出最佳的催化性能,所制得的催化剂表面会形成一层厚度约为3.5 nm的疏松多孔的锚定碳层,经100 h的单电池大电流老化测试后,锚定处理的PtRu/C功率密度只下降了12.0%,而未经锚定的PtRu/C下降了28.4%。为了进一步解决水热葡萄糖碳化包覆催化剂过程中,PtRu纳米颗粒不可逆的团聚现象,采用二次煅烧法制备了石墨相氮化碳/碳化学键合锚定型复合载体,PtRu/C@g-C_3N_4 NS催化剂的催化活性是PtRu/C的2.1倍。催化性能提高的原因主要包含以下方面:g-C_3N_4强的机械性能及在酸环境中高的稳定性;g-C_3N_4中富含的路易斯酸位及其他基团更易于锚定PtRu金属颗粒并减弱CO毒化中间产物在Pt活性位上的吸附强度;N-Pt之间强的电子修饰作用生成更多的催化活性位点。XC-72与尿素比例为1:2时所制备的催化剂有最佳的催化性能:尿素含量较低时,块状氮化碳在经过二次煅烧之后完全分解,失去载体对PtRu纳米颗粒的锚定作用,而尿素含量过高时,生成的氮化碳过多,会导致煅烧后氮化碳剥离不完全,催化剂导电性不足,性能变差。最佳的“二次煅烧时间”为2 h:处理时间较短时,外层的块状氮化碳不能剥离完全,催化剂因导电性差而失去催化活性;煅烧时间过长时,会使氮化碳过度分解,使催化剂纳米颗粒与氮化碳不能充分接触,不能起到载体对催化剂性能的促进作用。为进一步增强氮化碳与碳材料的接触程度,制备了氮化碳纳米片/石墨相碳键合锚定型复合载体。首先,利用氮化碳纳米片(尺寸为40 nm)与石墨烯相似的片状结构,通过π-π堆叠的方法设计并制备了r GO-(CN)锚定型载体材料,所制备的PtRu催化剂活性是PtRu/r GO的1.4倍,稳定性也明显提高。催化剂性能提升的主要原因是:g-C_3N_4 NS与石墨烯的层叠结构大幅提高了氮化碳的导电性;g-C_3N_4 NS更强的稳定性及其表面更多的含氮基团更易于锚定PtRu金属颗粒并防止中间毒化产物的累积;N-Pt之间强的电子相互作用。PtRu/r GO-(CN)中最佳的g-C_3N_4 NS含量为25%,因为随着氮化碳含量的增加,r GO表面被g-C_3N_4 NS覆盖的面积越大。当含量过低时,g-C_3N_4 NS对催化剂纳米颗粒的锚定作用及N-Pt电子作用不能充分发挥,使催化剂性能提升不足;但是当g-C_3N_4NS含量过高时,它会在石墨烯表面团聚和堆叠,导致催化剂导电性变差,PtRu纳米颗粒失去活性。其次,采用尺寸为20 nm的氮化碳纳米片与碳纳米管通过π-π堆积制备了CNT-CN化学键合锚定型载体,克服了传统酸处理碳纳米管材料结构不稳定、易腐蚀的缺点。相比传统的酸处理碳纳米管载PtRu催化剂,PtRu/CNT-CN催化剂催化活性提升1.3倍,稳定性有明显提升。这是由于碳纳米管完好结构带来的稳定性提升和g-C_3N_4 NS表面更多的含氮基团更易于锚定PtRu金属颗粒并修饰Pt外层电子结构使之更适合甲醇的催化氧化。最后,以介孔氮化碳为模板和氮源,直接在XC-72碳粉上沉积了导电性更高的Ti N纳米颗粒,制备出C-Ti N化学键合锚定型复合载体材料。实验结果表明:以介孔氮化碳/碳前驱体同时作为模板和氮源制备的C-Ti N锚定型载体具有较好的分散性,PtRu纳米粒子既可以与碳黑接触,也可以与Ti N充分接触;随着Ti N含量的增加,PtRu/C-Ti N催化剂的催化活性先升高再降低,而稳定性随着Ti N的提升变化不大。原因是Ti N含量过高会导致催化剂载体表面积大幅减小抑制PtRu颗粒的负载。综合考虑两者因素,PtRu/C-Ti N催化剂中最佳的Ti N占载体含量为15%。经过1000次的循环老化测试后,PtRu/C-Ti N-15%催化剂的催化活性是PtRu/C的1.5倍,稳定性也提高了6.5%。使用该载体制备的催化剂性能提升归因于Ti N与常用的碳载体相比具有更强的稳定性和Ti N与Pt颗粒之间有更强的锚定作用。
[Abstract]:Due to the rapid consumption of fossil energy in modern society and environmental pollution caused by the direct methanol fuel cell (DMFC) as a kind of green energy scheme attracted extensive attention of many scholars. However, the performance of PtRu anode catalyst in DMFC still could not meet the commercial requirements. In this paper, the "anchor PtRu particles" as the core, from the perspective of "physical coating anchor" and "chemical bonding anchor" direction and explore several high performance PtRu catalyst was prepared, and explain the reasons for the increase of the catalytic activity and stability were investigated in detail. Hydrothermal carbonization of glucose coating effect on the catalytic performance of PtRu/C catalysts for methanol. The study found that: the self-made PtRu/C catalyst after carbonization of glucose anchor after treatment, its stability is doubled. This is due to around PtRu nano alloy particles coated with a layer of more Stable carbon layer, metal particles on the surface of the carrier suppressed migration reunion; the other is because after the water after heat treatment, alloying degree of nano metal particles increased. In addition, the hydrothermal carbonization process, the catalyst surface will form a lot of help to enhance the catalyst of oxygen containing groups of anti poisoning ability, keep the initial catalytic the negative effects of high activity catalyst in the metal particle size grew up. When the water heat treatment time was 4 h, the carbon content is 9%, the catalyst showed the best catalytic performance of the catalysts, the surface will form a porous layer with a thickness of about 3.5 nm anchoring carbon layers. The single battery current 100 h aging test, PtRu/C power density anchor handling only dropped by 12%, but without the anchor of PtRu/C decreased by 28.4%. in order to further solve the hydrothermal carbonization of glucose coated catalyst in the process of nano PtRu Irreversible agglomeration of the particles, the two were prepared by calcination of graphite carbon nitride / carbon chemical bonding anchoraged composite carrier, PtRu/C@g-C_3N_4 catalytic activity of NS catalyst is 2.1 times that of PtRu/C. The reason for improvement of the catalytic performance mainly contains the following aspects: the mechanical properties of g-C_3N_4 high and high stability in acid environment g-C_3N_4; in the Lewis acid sites and other groups to anchor the PtRu metal particles and reduced CO poisoning intermediate product in the adsorption strength of Pt on active sites of the catalyst; the strong electronic modification of N-Pt between the generation of catalytic activity more sites of.XC-72 and urea proportion were prepared for 1:2 the best catalytic performance urea content is low, the massive carbon nitride after two times after calcination decomposed completely lost carrier on PtRu nanoparticles anchoring effect, while urea content is too high, too much carbon nitride That will lead to the calcined carbon nitride catalyst stripping is not complete, lack of conductivity, poor performance. The best "two calcination time" is 2 h:. The treatment time is short, the massive carbon nitride can not completely stripping the outer layers of the catalyst, because of poor conductivity and loss of catalytic activity; calcination time is too long, will make the nitride excessive carbon decomposition, make full contact of catalyst nanoparticles and carbon nitride can not play a role in promoting the carrier on the catalyst performance. In order to further enhance the contact degree of carbon nitride and carbon materials, carbon nitride nanosheets / graphite carbon bonded anchoraged composite carrier were prepared. Firstly, using nano carbon nitride film (the size is 40 nm) similar to the graphene sheet structure, through the method of Pi Pi stacking design and preparation of R GO- (CN) anchoraged carrier material, the activity of PtRu catalyst preparation is 1.4 times higher than that of PtRu/r GO, the stability is obviously improved. The main reason is: to improve the performance of catalyst NS and g-C_3N_4 laminated structure of graphene greatly improves the conductivity of carbon nitride; stability of g-C_3N_4 NS more and more surface nitrogen groups more easily anchored PtRu metal particles and prevent the accumulation of intermediate products of N-Pt poisoning; between the strong electronic interaction between.PtRu/r GO- (CN) g-C_3N_4 NS the best content is 25%, because with the increase of carbon nitride content, R GO g-C_3N_4 NS surface is covered a larger area. When the content is too low, g-C_3N_4 NS on the catalyst nanoparticles anchoring effect and N-Pt electronic can not fully play the role, so that the catalyst performance is insufficient; but when the g-C_3N_4NS content is too high when it will be on the surface of graphene agglomeration and stacking, lead to catalyst conductivity variation, PtRu nano particles lose activity. Secondly, the size of 20 nm carbon nitride nanosheets and carbon nanotubes using By stacking the preparation of CNT-CN chemical bond type anchor carrier, overcomes the material structure of the traditional acid treated carbon nanotubes is not stable, easy corrosion defects. Compared with the traditional acid treated carbon nanotubes supported PtRu catalysts, the catalytic activity of PtRu/CNT-CN catalyst is increased by 1.3 times, the stability has improved significantly. This is due to the stability of ascension and g-C_3N_4 NS brings to the surface of carbon nanotubes intact structure more nitrogen-containing groups more easily catalyzed oxidation of anchored PtRu metal particles and modified Pt outer electronic structure to make it more suitable for methanol. Finally, using mesoporous carbon nitride as template and nitrogen source, directly in the XC-72 toner deposited on Ti N nanoparticles with higher conductivity C-Ti N, prepared by chemical bonding anchoraged composite carrier material. The experimental results show that the mesoporous carbon nitride / carbon precursor as nitrogen source and template prepared C-Ti N anchoraged carrier has good points Dispersion, PtRu nanoparticles can contact with carbon black, can fully contact with the Ti N Ti; with the increase of N content, the catalytic activity of PtRu/C-Ti N catalyst increased firstly and then decreased, and the stability of Ti with the ascent of N changed little. The reason is high Ti N content will lead to catalyst surface area significantly reduced the inhibition of PtRu load particles. Considering the factors, PtRu/C-Ti N Ti N the best catalyst carrier for content was 15%. after 1000 cycles after the aging test, the catalytic activity of PtRu/C-Ti N-15% catalyst is 1.5 times that of PtRu/C, the stability of high performance 6.5%. catalyst for the preparation of the carrier to enhance more than Ti N between attribution compared with the commonly used carbon carrier has stronger stability and Ti N and Pt particles in the anchoring effect.

【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;TM911.4

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