乙醇电氧化催化剂制备及其反应机理研究

发布时间：2018-03-10 00:30

  本文选题：直接乙醇燃料电池　切入点：原位电化学质谱　出处：《哈尔滨工业大学》2017年博士论文　论文类型：学位论文

【摘要】：直接乙醇燃料电池阳极催化剂的研究对其商业化应用具有非常重要的意义,开发具有高活性和稳定性,同时具备高的电氧化效率的催化剂至关重要。乙醇电氧化的主要产物为乙醛和乙酸,想通过合理设计催化剂促进乙醇氧化生成更多二氧化碳,需要对乙醇的电氧化机理和产物进行有效分析。本论文从电催化剂结构设计和组分调整出发,结合差分电化学质谱方法,解析催化剂微观结构和组分对乙醇电氧化产物和机理的影响,从而实现对电催化剂设计的指导。采用紫外光还原法合成p-Pt-TiO_2-rGO复合材料,这种材料具备铂-二氧化钛-石墨烯三相接触结构。首先合成石墨烯载二氧化钛纳米颗粒复合材料,二氧化钛纳米颗粒均匀分散于石墨烯片层表面;随后在碱性条件下,通过紫外光激发二氧化钛产生电子将氯铂酸根离子还原成铂纳米颗粒。XRD和TEM表征表明紫外光还原法得到的铂纳米颗粒(平均粒径为2.2 nm)易于沉积在二氧化钛纳米颗粒和石墨烯片层之间,从而形成铂-二氧化钛-石墨烯两两接触的三相接触结构。紫外光还原法制备的p-Pt-TiO_2-rGO表现出比微波乙二醇法制备的m-Pt-TiO_2-rGO和m-Pt/rGO更高的乙醇电氧化活性。老化测试结果证明电催化剂p-Pt-TiO_2-rGO耐久性是m-Pt-TiO_2-rGO和m-Pt/rGO的两倍以上。XPS测试表明p-Pt-TiO_2-rGO电催化剂相对于m-Pt-TiO_2-rGO表现出更强的铂与载体相互作用,这促进了毒化中间产物的移除,阻碍了铂纳米颗粒的迁移/团聚或从碳载体上的分离。而原位电化学质谱分析表明,铂与二氧化钛的紧密复合可以促进乙醇解离吸附反应生成乙酸,同时不利于乙醇的C-C键断裂。采用L-精氨酸诱导法合成具备铂-二氧化锡-石墨烯三相接触结构的Pt/SnO_2/rGO电催化剂。首先利用Sn2+的还原性和氧化石墨的氧化性,原位发生氧化还原反应制备石墨烯载二氧化锡纳米颗粒复合材料,二氧化锡纳米颗粒均匀分散于石墨烯片层表面;随后用L-精氨酸修饰二氧化锡纳米颗粒,L-精氨酸作为保护剂和连接剂,诱导铂纳米颗粒原位沉积在二氧化锡纳米颗粒周围,并且防止铂纳米颗粒的团聚。制备得到的Pt/SnO_2/rGO电催化剂表现出优良的乙醇电氧化活性和稳定性:Pt/SnO_2/rGO电催化剂乙醇电氧化CV正扫峰电流是Pt/rGO的4.5倍;经过1000次循环老化测试后,Pt/SnO_2/rGO电催化剂乙醇电氧化活性的保持率在69.6%,远高于Pt/rGO的41.1%,这主要归因于Pt/SnO_2/rGO电催化剂中的二氧化锡促催化作用和铂-二氧化锡-石墨烯两两接触的三相接触微观结构。原位电化学质谱分析表明,Pt/SnO_2/rGO电催化剂不利于乙醇分子C-C键断裂和完全氧化,二氧化锡的引入提高了乙醇电氧化生成乙醛的电流效率,降低了电氧化生成乙酸和二氧化碳的电流效率,因此具有更低的乙醇电氧化电流效率。从微观结构方面出发,设计开发了三明治状结构的SnO_2/Pt/rGO电催化剂,并研究其对乙醇电氧化反应活性和效率的影响。首先研究了不同石墨烯含量对乙醇电氧化活性的影响,当石墨烯质量分数为30%时活性最高,其次是40%和20%。电化学研究表明SnO_2/Pt/rGO电催化剂相对于Pt/rGO表现出更好的乙醇电氧化活性和稳定性:SnO_2/Pt/rGO电催化剂乙醇电氧化CV正扫峰电流是Pt/rGO的1.31倍;经过2000次加速老化测试后,SnO_2/Pt/rGO电催化剂乙醇电氧化活性的保持率在75.9%,远高于Pt/rGO的48.1%,这主要归因于SnO_2/Pt/rGO电催化剂中的三明治状微观结构。原位电化学质谱分析表明,电催化剂SnO_2/Pt/rGO具备与Pt/rGO 一致的生成二氧化碳电流效率,这意味着相对于具备铂-二氧化锡-石墨烯两两接触的三相接触结构的Pt/SnO_2/rGO电催化剂,电催化剂SnO_2/Pt/rGO具备更强的C-C键断裂能力。这是因为三明治状的微观结构促进了乙醇电氧化中间产物乙醛和乙酸的进一步氧化,增加了乙醛和乙酸重新进入电化学反应活性区的几率,提高了生成二氧化碳和乙酸电流效率,降低了生成乙醛电流效率,促进了乙醇的完全氧化。从组分调整的角度出发,引入了具备强的C-C键断裂能力的Ir元素,研究了 PtIr对乙醇电氧化效率的影响。Ir对于乙醇分子的C-C键断裂具有十分显著的作用,铂铱合金对乙醇电氧化生成二氧化碳的电流效率提高10%左右。
[Abstract]:Study on anode catalysts for direct ethanol fuel cell has a very important significance for the development of commercial applications, with high activity and stability of catalysts is very important also have high efficiency of electro oxidation. The main products of the electro oxidation of ethanol to acetaldehyde and acetic acid, want to through the reasonable design of catalyst for ethanol oxidation to produce more carbon dioxide, need for effective analysis the electro oxidation mechanism and products of ethanol. The adjustment from the electrocatalyst structure design and the group of combination of differential electrochemical mass spectrometry, microstructure and analytical catalyst effects on ethanol electro oxidation products and mechanism, thus realizing the guidance of electrocatalyst design. The p-Pt-TiO_2-rGO composite material was synthesized by reduction of UV light. This material has the Pt-TiO2 graphene three-phase contact structure. The first synthesis of graphene supported nano titanium dioxide Composite particles, TiO2 nanoparticles dispersed on the surface of graphene sheets; then under alkaline conditions, the platinum chloride ion electron reduction of platinum nanoparticles.XRD and TEM characterization showed that platinum nanoparticles obtained by UV reduction titanium dioxide ultraviolet excitation (average particle size 2.2 nm) is deposited between titanium dioxide nanoparticles and graphene layers, thus forming the three-phase contact structure Pt-TiO2 graphene 22 contact. UV reduction prepared by p-Pt-TiO_2-rGO showed ethanol electro oxidation activity than microwave glycol prepared by m-Pt-TiO_2-rGO and m-Pt/rGO. The higher the aging test results prove that the electrocatalyst durability of p-Pt-TiO_2-rGO is m-Pt-TiO_2-rGO and m-Pt/rGO two more than.XPS tests show that p-Pt-TiO_2-rGO catalysts compared with m-Pt-TiO_2-rGO showed stronger and platinum loading Body interaction, which promotes the poisoning of the intermediate products removed, hinder the migration / platinum nanoparticle aggregation or separation from the carbon carrier. And in situ electrochemical mass spectrometry analysis showed that platinum and titanium dioxide composite closely can promote the dissociative adsorption of ethanol reacts with acetic acid, is not conducive to the breaking of C-C bonds with L- ethanol. Arginine induced synthesis of Pt/SnO_2/rGO electro catalyst platinum - two tin oxide graphene structure. Firstly, the three-phase contact oxidation of Sn2+ and reduction of graphite oxide, in situ redox reaction in the preparation of graphene containing two tin oxide nano particle composite material, two tin oxide nanoparticles dispersed on graphene the lamellar surface; followed by L- arginine modified two tin oxide nanoparticles, L- arginine as a protective agent and coupling agent, induced by platinum nanoparticles in situ deposited around two tin oxide nanoparticles, And to prevent the platinum nanoparticle aggregation. The prepared Pt/SnO_2/rGO catalyst showed excellent ethanol electro oxidation activity and stability: Pt/SnO_2/rGO electrocatalysts for ethanol electro oxidation of CV is to sweep the peak current is 4.5 times that of Pt/rGO; after 1000 cycles of aging test, Pt/SnO_2/ rGO electrocatalysts for ethanol electro oxidation activity retention rate of 69.6% 41.1%, much higher than the Pt/rGO, three-phase two tin oxide which is mainly attributed to Pt/SnO_2/rGO in the catalyst catalyzed and platinum - two tin oxide graphene 22 contact microstructure. In situ electrochemical mass spectrometry analysis showed that the Pt/SnO_2/rGO catalyst is not conducive to ethanol molecules C-C bond cleavage and complete oxidation, introduced two tin oxide to improve the current efficiency of the electro oxidation of ethanol to acetaldehyde, reduces the current efficiency of the electrochemical oxidation of acetic acid and carbon dioxide, so the electro oxidation of ethanol has a lower The current efficiency. Starting from the microscopic structure, design and development of the SnO_2/Pt/rGO electrocatalyst sandwich structure, and study its effect on ethanol electro oxidation reaction activity and efficiency. Firstly, the effects of different content of graphene on the ethanol electro oxidation activity, when the mass fraction of graphene was 30% was the highest, followed by 40% the electrochemical study shows that SnO_2/Pt/rGO and 20%. electrocatalysts exhibited better than Pt/rGO ethanol electro oxidation activity and stability: SnO_2/Pt/rGO electrocatalysts for ethanol electro oxidation of CV is to sweep the peak current is 1.31 times that of Pt/rGO; after 2000 times of accelerated aging test, SnO_2/Pt/rGO electrocatalyst ethanol electro oxidation activity retention rate of 75.9%, much higher than the Pt/rGO 48.1% sandwich structure, which is mainly attributed to SnO_2/Pt/rGO in the catalyst. In situ electrochemical mass spectrometry analysis showed that the SnO_2/Pt/rGO electrocatalyst has 涓嶱t/rGO 涓，

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