紫菜基分级多孔炭的制备及其在氧还原反应中的应用

发布时间：2018-05-06 22:35

  本文选题：紫菜 + 分级多孔炭　； 参考：《北京化工大学》2017年硕士论文

【摘要】：多孔炭材料具有比表面积高、孔隙发达、导电导热性能好等特点,被广泛应用于能量转化与储存、工业催化、气体吸附和分离等领域。近年来发展的具有微孔-介孔-大孔三维贯通的分级多孔炭材料,可以大幅度地提高反应物/生成物的传质,进而促进电化学反应过程,因而在氧还原反应中具有良好的应用前景。生物质材料富含碳、氮、磷等元素,可再生、来源广泛,是制备分级多孔炭的理想前驱体,本文采用廉价易得的红藻类植物---紫菜为前驱体,通过对炭化和活化工艺条件的调控,制备出系列分级多孔炭材料,揭示了紫菜的成碳机制。在此基础之上,开展了紫菜炭作为氧还原反应催化剂载体的应用研究。本论文的主要创新工作如下:一、以紫菜为前驱体,通过预碳化、碳化活化制备了高比表面积且具有微孔-介孔-大孔三维连通的蜂窝状孔道结构的氮掺杂分级多孔炭材料。研究表明,紫菜中富含的蛋白质和多糖是主要的碳、氮前驱体,紫菜中所含的无机盐可作为天然模板在活化过程中进一步调控孔道结构。当预碳化物与活化剂质量比为2,碳化活化温度为900℃时,制备的分级多孔炭比表面积最高(2152.5 m2g-1),孔容为1.03 cm3 g-1,孔结构以微孔为主(占比91.6 %),氮含量为1.8 at.%。二、以制备的紫菜基多孔炭为载体,通过吸附以及低温热处理分散的方法,负载具有高活性Fe(Ⅱ)-N4中心的酞菁铁分子,制得紫菜基多孔炭负载酞菁铁的分子级铁、氮共掺杂分级多孔炭催化剂。同时考察了炭载体、酞菁铁负载量等对催化剂性能的影响,发现紫菜基多孔炭的分级多孔结构和表面氮掺杂结构,有利于提高酞菁铁分子的负载量,同时增强酞菁铁分子和载体之间的相互作用,从而提高其氧还原催化性能。电化学测试表明,400 ℃热解制备的分子级催化剂氧还原半波电位为0.88 Vvs. RHE,比商业化Pt/C高40 mV,电子转移数为4,为理想的4电子反应。该催化剂经3000圈循环稳定性测试后,半波电位仅负移6 mV,具有优于商业化Pt/C的电化学稳定性。三、根据微孔结构和表面掺杂结构对原子级活性中心的约束作用,进一步采用血晶素为天然铁/氮源,紫菜基多孔炭为载体,通过吸附以及高温热解还原的方法,将原始血晶素中低催化活性的Cl-Fe(Ⅲ)-N4结构,在800 ℃时热解还原成与炭载体紧密相连的高活性原子级Fe-NxCy催化中心,同时该催化剂表现出铁原子高度均匀分散的特点。通过电化学测试表明,该原子级催化剂的半波电位达到0.87 V vs. RHE,高于Pt/C 30 mV,动力学电流密度(Jk@ 0.88 V vs.RHE)高达4.1mA cm-2,同时具有显著优于Pt/C的稳定性和抗甲醇毒化能力。由于血晶素中有机相的高温热解炭化,该原子型催化剂中的铁原子和炭载体紧密相连,相比与之前的分子型催化剂,表现出更强的催化稳定性(3000圈稳定性实验后半波电位仅负移1 mV)。
[Abstract]:Porous carbon materials have been widely used in energy conversion and storage, industrial catalysis, gas adsorption and separation due to their high specific surface area, well developed pores and good conductivity and thermal conductivity. Recently developed porous carbon materials with microporous mesoporous and macroporous three dimensional permeation can greatly improve the mass transfer of reactants / products and thus promote the electrochemical reaction process. Therefore, it has a good application prospect in oxygen reduction reaction. Biomass materials are rich in carbon, nitrogen, phosphorus and other elements. They can be regenerated and come from a wide range of sources. They are ideal precursors for the preparation of graded porous carbon. In this paper, the cheap and easily available red-algae -porphyra was used as the precursor. A series of graded porous carbon materials were prepared by controlling the carbonization and activation conditions, which revealed the carbonation mechanism of porphyra yezoensis. On this basis, the application of porphyra charcoal as catalyst carrier for oxygen reduction reaction was studied. The main innovative work of this thesis is as follows: 1. The nitrogen-doped porous carbon materials with high specific surface area and three dimensional connectivity of microporous mesoporous and macroporous channels were prepared by carbonization and carbonization with porphyra yezoensis as precursor. The results showed that the protein and polysaccharide rich in porphyra were the main precursors of carbon and nitrogen. The inorganic salts contained in the porphyra could be used as natural templates to further regulate the pore structure in the process of activation. When the mass ratio of precarbide to activator is 2 and the activation temperature of carbonation is 900 鈩，

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