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题名: 新型氧还原电极制备及其催化净水性能与机制研究
作者: 孙猛
学位类别: 博士
答辩日期: 2016-05
授予单位: 中国科学院研究生院
授予地点: 北京
导师: 曲久辉
关键词: 电催化 ; Electrocatalysis ; 氧气还原 ; Oxygen reduction ; 电极材料 ; Cathode material ; 过氧化氢 ; Hydrogen peroxide ; 水处理 ; Water treatment
其他题名: Novel Oxygen Reduction Electrodes: Preparation, Performance and Mechanism on Its Catalytic Water Purification
学位专业: 环境工程
中文摘要:       阴极氧气还原反应(ORR)可分为两个不同的动力学过程:(1)两步两电子还原路径,过氧化氢为主要中间产物;(2)直接四电子还原途径,最终产物为水。依据两电子路径,ORR 可用于工业合成过氧化氢等化工领域;基于四电子途径,其可在燃料电池等能源转化与存储和化学防腐等领域发挥作用。然而,传统的铂基ORR 催化剂已难以满足低成本催化剂的应用需求,开发更为高效、稳定及高反应选择性的电极材料,成为近年来研究的热点。
      本文针对传统阴极ORR 催化剂动力学迟缓和催化稳定性差等不足,制备了多种过渡金属类/碳材料及贵金属类/碳材料复合纳米电极材料用于高效阴极电催化氧气还原反应,并依据电分析化学手段解析电极表面电催化ORR 动力学过程,确立了适用于水处理领域的高效ORR 阴极纳米材料的设计方法;最终构建出三维电催化水处理体系,在原位电催化氧气还原合成H2O2、催化氧化有机污染物、重金属氧化还原转化、吸附有色有机物及有机物还原等重要反应中表现出优异的催化活性,展现出良好的应用前景。
      首先,制备开发了一系列含铁的碳基复合材料,探讨了复合物组成、结构对氧还原反应路径的影响。基于旋转圆盘电极(RDE)伏安法在不同转速下的Koutecky-Levich 曲线,测算出α-Fe2O3/N-CNTs 电极表面的氧气还原电子转移数为3.37,说明其表面ORR 动力学过程接近直接4 电子还原路径,H2O 为主要还原产物。基于旋转圆盘圆环电极(RRDE)伏安法,间接通过圆环电流变化测得Fe-N-C-800 电极的氧还原n 值为3.7,近似4 电子还原过程。而Fe-N-C-700 的n仅为3,说明其ORR 过程介于2 电子与4 电子之间,其高达42%的H2O2 产率更适宜作为原位选择性氧还原合成H2O2 的阴极材料。
      其次,进一步考察了低负载量贵金属/碳基复合电极材料原位氧还原合成H2O2 性能与应用。采用一步化学还原法制备了AuPd/CNTs 粒子电极材料。结果证明,Au 的引入保护了合金的活性(111)晶面,促进了电极的电催化ORR 性能,主要表现在可使O2 在其表面以2.68 个电子还原路径高效合成H2O2,致使60 min 时H2O2 浓度达到0.37 mM。进一步通过低温化学还原法优化AuPd/CNTs的形貌和催化性能,制备了合金尺寸更小、分布更均一的M-AuPd/CNTs 纳米粒子电极。M-AuPd/CNTs 在酸性条件下具有更高的电催化ORR 响应,ORR 动力
学电子转移数最低为2.25,H2O2 的产率高达84.43%。通过对AuPd/CNTs 电极形貌和结构优化,逐步调控其表面电催化氧气还原电子转移过程,揭示了电极“形貌-结构-性能”三者之间的内在联系。基于AuPd/CNTs 和M-AuPd/CNTs 粒子电极的电催化体系分别在原位Fe2+再生、催化氧化水体有机污染物以及重金属砷、铬协同共转化中发挥了积极作用。粒子电极具有较好的沉降性,使其循环利用10 次时对有机物矿化及重金属共转化的效率仍高于95%。
      再次,为了进一步提高三维电极体系电流传导效率并优化电极结构,推动新型电化学集成组件的研究,采用水热合成法制备了AuPd/3DGFEs 三维立体网络结构电极及其氮掺杂的AuPd/N-3DGFEs 电极。结果表明,三维石墨烯基底具有网络互通的孔隙结构,可为活性AuPd 合金纳米球负载提供稳固、导电性好、比表面积高的载体,提高其与溶液中反应物质的接触几率。氮的掺杂一方面增加石墨烯内表面的褶皱程度,强化电极传质效率的同时也增加了电极表面氧、氮的存在形式,为催化反应提供更多的活性缺陷位点。致使AuPd/N-3DGFEs 与AuPd/3DGFEs 电催化ORR的n 值分别为2.7 和2.6,H2O2产率分别为62%和65%。在此基础上,探索了基于AuPd/3DGFEs 电极的电催化水处理连续流反应器对原位电催化合成H2O2 及砷、铬共转化,电催化吸附亚甲基蓝,电催化还原转化硝基苯与4-硝基苯酚等重要反应的应用,新型反应器的高催化活性和良好稳定性表明其广泛的应用前景。
英文摘要:       The oxygen reduction reaction (ORR) can proceed either via (1) a direct four-electron pathway to produce water as the end product or (2) a two-step two-electron process with the formation of hydrogen peroxide (H2O2) in acidic solution, which can be applied to the chemical synthesis and production of H2O2. However, platinum based electrocatalysts cannot meet the demands of developing eco-friendly and sustainable ORR catalysts due to their prohibitive cost and scarcity in nature. Therefore, exploring low-cost and highly efficient ORR electrocatalysts has become the advanced research hotspot.
      Transition metal/carbon and noble metal/carbon nanocomposite cathodes with enhanced ORR activity and desirable catalytic durability were synthesized to overcome the shortage of sluggish ORR kinetic and stability. The kinetic process of ORR on these electrodes was carefully investigated by virtue of the electrochemical analysis method, in order to reveal their ORR property. On these bases, the three-dimensional electrocatalysis water treatment system contributed to the in-situ catalytic synthesis of H2O2, oxidation of organic pollutants, redox conversion of heavy metals, adsorption of color organics and reduction of toxic organic compounds. Moreover, those electrodes also exhibit excellent feasibility economically.
The kinetic ORR electron transfer number (n) can be calculated as 3.37 for α-Fe2O3/N-CNTs from the Rotating Disk Electrode (RDE) voltammetry analysis under different rotation rates in O2-saturated solution. The results also indicated that the α-Fe2O3/N-CNTs electrode facilitated an approximate four-electron reduction pathway. Furthermore, by means of the Rotating Ring Disk Electrode (RRDE)voltammetry, different disk currents suggested the average n value was 3.7 for the prepared Fe-N-C-800 catalysts. However, the n value of Fe-N-C-700 was calculated to be 3, suggesting that Fe-N-C-700 possessed a moderate two and four electrons ORR pathway to form H2O2. The generation rate of H2O2 of Fe-N-C-700 was 42%.
      AuPd/CNTs nanocatalysts were successfully synthesized by the crystallization of AuPd alloys via facile chemical reduction method. XRD and XPS characterizations provided structural insights that Au strengthened the construction of AuPd alloys, immobilizing the active AuPd (111) facets. Those nanocatalysts ensured pleasurable ORR kinetic process, achieving 2.68 electrons reduction route and resulting in the generation of H2O2 of 0.36 mM within 60 min. Moreover, the modified-AuPd/CNTs (M-AuPd/CNTs) with optimized morphology and catalytic activity were further produced. The M-AuPd/CNTs was proved to have low onset and peak potentials for ORR and enable 2.25 electrons reduction pathway, leading to the efficient H2O2 generation rate of 84.43%. On account of this, the superior in situ Fe2+ regeneration, the electrocatalytic degradation of DMAC and phenol, and the synergistic redox conversion of Cr(VI) to Cr(III) and As(III) to As(V) were efficiently achieved via the
three-dimensional electrocatalysis system by using AuPd/CNTs and M-AuPd/CNTs electrocatalysts, respectively. These cathode materials exhibited good stability and
durability after 10 times reuse.
      To further improve the structure and organization of three-dimensional electrodes from the decentralized interaction to centralized form, the AuPd alloys anchored three-dimensional graphene framework electrodes (AuPd/3DGFEs) and nitrogen doped AuPd/3DGFEs (AuPd/N-3DGFEs) were prepared. The TEM, Raman, and XPS characterizations indicated the nitrogen doping leads to porous structure and various oxygen and nitrogen contained groups on graphene surface, which accelerated ORR activities of both AuPd/3DGFEs and AuPd/N-3DGFEs with the n value of 2.6 and 2.7, respectively, resulting in the high H2O2 generation rate of 65% and 62%. The AuPd/3DGFEs electrocatalysis continuous flow reactor shows promising applied catalytic applicability in H2O2 synthesis, redox conversion of Cr(VI) and As(III), and decoloration of methylene blue and catalytic reduction of nitro-compounds.
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/36956
Appears in Collections:环境水质学国家重点实验室_学位论文

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Recommended Citation:
孙猛. 新型氧还原电极制备及其催化净水性能与机制研究[D]. 北京. 中国科学院研究生院. 2016.
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