催化学报

催化学报 ›› 2015, Vol. 36 ›› Issue (8): 1197-1204.DOI: 10.1016/S1872-2067(15)60912-3

• 论文 • 上一篇    下一篇

热解条件对氮杂有序介孔炭材料电催化性能的影响

龙桂发a, 万凯a, 刘明尧a, 李小花a, 梁振兴a, 朴金花b   

  1. a 华南理工大学化学与化工学院, 广东省燃料电池技术重点实验室, 广东广州510641;
    b 华南理工大学轻工与食品学院, 广东广州510641
  • 收稿日期:2015-03-03 修回日期:2015-05-21 出版日期:2015-07-29 发布日期:2015-07-30
  • 通讯作者: 梁振兴
  • 基金资助:

    国家自然科学基金(21476087); 广州市珠江科技新星专项(2013J2200041); 广东省科技计划项目(2014A010105041); 广东省自然科学基金(S2013010012469); 广东省教育厅特色创新项目(2014KTSCX016).

Effect of pyrolysis conditions on nitrogen-doped ordered mesoporous carbon electrocatalysts

Guifa Longa, Kai Wana, Mingyao Liua, Xiaohua Lia, Zhenxing Lianga, Jinhua Piaob   

  1. a Key Laboratory on Fuel Cell Technology of Guangdong Province, School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510641, Guangdong, China;
    b School of Light Industry and Food Science, South China University of Technology, Guangzhou 510641, Guangdong, China
  • Received:2015-03-03 Revised:2015-05-21 Online:2015-07-29 Published:2015-07-30
  • Supported by:

    The work was supported by the National Natural Science Foundation of China (21476087), Pearl River S&T Nova Program of Guangzhou (2013J2200041), the Science & Technology Research Project of Guangdong Province (2014A010105041), Guangdong Natural Science Foundation (S2013010012469), and Innovation Project of Guangdong Department of Education (2014KTSCX016).

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885

被引次数

11

摘要：

氧还原反应是燃料电池及金属空气电池中极其重要的电化学反应之一, 贵金属铂基催化剂被认为是最有效的氧还原反应电催化剂. 然而, 贵金属铂的资源稀缺以及高成本问题阻碍了相关技术的大规模应用, 探索发展廉价高效的贵金属替代型催化剂是推动燃料电池发展的根本解决方案. 近年来, 人们在非贵金属催化剂开发方面取得了显著进展, 其中新型纳米结构掺杂炭材料研究尤为活跃. 氮杂有序介孔炭材料由于其高比表面积和独特的孔结构, 在燃料电池技术上具有广泛的应用前景. 在氮杂有序介孔炭材料的制备过程中, 热解条件对炭材料组成、结构及电催化性能有着重要影响. 然而, 目前尚未见对氮杂炭材料制备过程中热解条件的影响进行系统研究.
本文采用我们发展的蒸汽化-毛细管冷凝法, 以SBA-15为硬模板浸渍前驱体吡咯, 制备出具有高比表面积和独特孔结构的氮杂有序介孔炭材料, 系统研究了热解条件(包括热解温度、热解时间和升温速率)对炭材料组成、结构及电催化性能的影响, 采用N2吸附-脱附等温线、X射线光电子能谱(XPS)及 Raman光谱等方法考察了氮杂有序介孔炭材料的结构和组成, 采用循环伏安法与旋转环盘电极研究了其电化学行为与氧还原反应电催化活性及选择性.
N2吸附-脱附等温线显示, 氮杂炭材料对应IV型吸附-脱附等温线, 孔径主要分布在2-10 nm, 表明所制材料具有介孔结构. 随着热处理温度升高, 氮杂有序介孔炭材料比表面积先增加而后降低, 热处理时间的延长有利于比表面积增大, 但升温速率对所制炭材料比表面积没有明显影响, 当升温速率为30 ℃/min, 900 ℃焙烧3 h时, 氮杂有序介孔炭材料的比表面积达到最大值888 m2/g. XPS测试结果表明, 随着热处理温度升高, 氮杂有序介孔炭材料中含氮基团的分解进一步加深, 使N含量逐渐降低. 延长热处理时间亦然, 而升温速率的改变对N含量无明显影响. 在热处理温度较低时(600 ℃), 所得材料中N主要以吡咯氮和吡啶氮的形式存在; 当温度达到800 ℃以上, 吡咯氮转化为吡啶氮和骨架氮, 且主要以骨架氮形式存在, 说明氮杂有序介孔炭材料的石墨化程度逐渐升高. Raman光谱结果显示, 随着热处理温度升高, ID/IG逐渐降低, 进一步印证了温度对石墨化程度的影响.
电化学测试结果表明, 随着热处理温度升高, 氮杂有序介孔炭材料的氧还原反应电催化活性逐渐升高, 但是当热处理温度从900 ℃升至1000 ℃时, 氧还原反应活性增加很小; 升温速率与热处理时间对氧还原反应电催化活性的影响均不明显. 与商品Pt/C催化剂相比, 900 ℃以上所制催化剂均表现出更优异的氧还原电催化活性与选择性. 由此可见, 热处理温度是决定碳源热化学行为的关键因素, 进而决定炭材料表面组成与结构. 电化学研究结果表明, 800 ℃以上进行热处理碳化, 所生成石墨化微晶可有效促进电子传递, 降低欧姆极化损失, 同时, 较高的处理温度可促进骨架氮掺杂, 从而构建出高效氧还原反应活性位点. 因此, 氮杂型炭催化剂的组成、结构与电化学性能更多地受控于热处理过程中的热力学, 而非热解动力学过程.

关键词: 电催化剂, 氮掺杂炭, 有序介孔材料, 氧还原反应, 热解条件

Abstract:

Pt is the most effective and widely used electrocatalyst for the oxygen reduction reaction (ORR) in fuel cells; however, its scarcity and high cost pose a great challenge to the commercialization of the fuel cell technology. N-doped carbon materials have been regarded as one of the most promising Pt-alternative catalysts. In this work, the N-doped ordered mesoporous carbon was synthesized by the nanocasting method using SBA-15 as the template. The effect of the pyrolysis conditions (pyrolysis temperature, pyrolysis duration, and ramp rate) on this material was investigated. N2 adsorption-desorption isotherms, X-ray photoelectron spectroscopy, and Raman spectroscopy were used to investigate the intrinsic properties of the resultant materials. Cyclic voltammetry and rotating ring-disk electrode were used to investigate the electrochemical behavior for ORR in an alkaline medium. It was found that the resultant mesoporous carbon materials exhibit high electrical conductivity, high specific surface area, and unique pore structure. The pyrolysis temperature was the most important parameter in determining the thermodecomposition of the carbon precursor, and the microstructure, elemental composition, and chemical configuration of the resultant mesoporous carbon materials. To achieve reasonable electrocatalytic activity and selectivity, a high pyrolysis temperature above 800 ℃ is required for effective N doping to form active sites and for graphitization to facilitate charge transfer, whereas the pyrolysis duration and ramp rate have a much less significant effect. This indicates that both the surface composition/structure and consequent electrochemical properties are more dependent on the thermodynamics than the kinetics during the pyrolysis process. Finally, the optimal N-doped ordered mesoporous carbon catalyst showed superior electrochemical activity for ORR than the commercial Pt catalyst and is promising for fuel cell and metal-air battery applications.

Key words: Electrocatalyst, Nitrogen-doped carbon, Ordered mesoporous material, Oxygen reduction reaction, Pyrolysis condition