催化学报 ›› 2016, Vol. 37 ›› Issue (7): 1096-1102.DOI: 10.1016/S1872-2067(15)61063-4

• 论文 • 上一篇    下一篇

聚对苯二胺和炭黑复合物作为高效的氧还原催化剂及其稳定性研究

苏小钢a,b, 姚颖方a,b,c, 田娟c, 刘建国a,b,c,d, 汪忠伟a,b, 尤勇a,b, 黄林a,b,c, 吴聪萍a,b,c   

  1. a. 南京大学现代工程与应用科学学院, 江苏 南京 210093;
    b. 南京大学固体微结构物理国家重点实验室, 人工微结构科学与技术协同创新中心, 江苏 南京 210093;
    c. 南京大学昆山创新研究院, 江苏 昆山 215347;
    d. 南京大学 (苏州) 高新技术研究院, 江苏 苏州 215123
  • 收稿日期:2016-01-06 修回日期:2016-02-02 出版日期:2016-06-17 发布日期:2016-06-17
  • 通讯作者: Jianguo Liu
  • 基金资助:

    国家自然科学基金(21476104);江苏省自然科学基金杰出青年基金(BK20150009);江苏省自然科学基金青年基金(BK20150396);江苏省软科学研究项目(BR2015009);江苏省苏州市纳米技术专项(ZXG2013029);江苏省优势学科以及江苏省青蓝工程资助;中央高校基本科研业务费.

Investigation of the durability of a poly-p-phenylenediamine/carbon black composite for the oxygen reduction reaction

Xiaogang Sua,b, Yingfang Yaoa,b,c, Juan Tianc, Jianguo Liua,b,c,d, Zhongwei Wanga,b, Yong Youa,b, Lin Huanga,b,c, Congping Wua,b,c   

  1. a. College of Engineering and Applied Sciences, Nanjing University, Nanjing 210093, Jiangsu, China;
    b. National Laboratory of Solid State Microstructures, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, Jiangsu, China;
    c. Kunshan Innovation Institute of Nanjing University, Suzhou 215347, Jiangsu, China;
    d. Suzhou High-Tech Institute of Nanjing University, Suzhou 215123, Jiangsu, China
  • Received:2016-01-06 Revised:2016-02-02 Online:2016-06-17 Published:2016-06-17
  • Contact: Jianguo Liu
  • Supported by:

    This work was supported by the National Natural Science Foundation of China (21476104), the Natural Science Foundation for Distinguished Young Scholars of Jiangsu Province (BK20150009), the Natural Science Foundation for Young Scholars of Jiangsu Province (BK20150396), the Soft Science Research Program of Jiangsu Province (BR2015009), the Nanotechnology Program of Suzhou (ZXG2013029), the Priority Academic Program Development (PAPD) of Jiangsu Higher Education Institutions, Qing Lan Project of Jiangsu Province, and the Fundamental Research Funds for the Central Universities, China.

摘要:

近年来,氮掺杂的碳材料作为碱性氧还原催化剂得到了研究者的广泛关注.掺杂的N原子会影响C原子的自旋密度和电荷分布,导致碳材料表面产生"活性位点",因此掺氮碳材料具有优秀的氧还原活性,这已经在理论计算和实验中得到了验证.我们通过调节聚对苯二胺和碳黑的比例,之后进行热解制备了一系列掺氮碳材料.其中0.88PpPD/CB样品具有最好的氧还原活性,其在KOH溶液(0.1mol/L)中的氧还原性能超过了商业碳载铂.通过扫描电子显微镜表征,发现碳球聚集在聚对苯二胺的表面,这主要是因为聚对苯二胺没有进行酸掺杂,因此其水溶性比较差.通过氮气的吸脱附表征,发现聚对苯二胺的比表面积很小,而碳黑样品(BP2000)的比表面积很大.因此,随着聚对苯二胺量的增加,聚对苯二胺/碳黑复合物的比表面积逐渐降低.另外,聚对苯二胺表面几乎都是微孔,而介孔和大孔主要来自于碳黑.研究者认为,"活性位点"主要位于微孔内(聚对苯二胺表面),而介孔和大孔有利于物质的传输.因此,当聚对苯二胺和碳黑的比例合适时,既有大量的"活性位点"暴露,又有足够的介孔和大孔进行物质传输,所以0.88PpPD/CB样品的氧还原活性最高.但是,对于掺氮碳材料来说,一个主要的问题就是稳定性不足.不管是电化学稳定性,还是放置在空气中的稳定性,掺氮碳材料都比不上铂基催化剂,这也阻碍了它们的大规模应用.对于电化学稳定性,很多文章都进行了报道,但是很少有文章报道掺氮碳材料在空气中的稳定性.我们知道,铂基材料之所以具有优异的氧还原活性,是因为铂和氧气的结合能比较合适,既利于氧气吸附,也利于之后氧气分子键的断裂.但是,当铂基材料放置在空气中,氧气的吸附也会发生,而且之后会导致表面氧化层的形成.所以铂基材料需要活化才能达到最好的催化性能.对于掺氮碳材料,放置在空气中会不会发生氧化反应?这对氧还原活性是否有影响?为了研究掺氮碳材料在空气中的稳定性,我们将0.88PpPD/CB样品在空气中放置了一个月,之后再进行电化学测试.旋转圆盘电极测试表明,在空气中放置了一个月后,0.88PpPD/CB样品的氧还原活性降低了,不管是半波电位还是极限电流密度都下降了.之后我们对其进行了X射线光电子能谱检测,发现在空气中放置了一个月后其氧含量提高了1%(原子分数),而氮含量几乎没有变化.氧含量的提高证实了氧化反应的发生,但不能直接归结于空气中的氧气.为了排除其他因素,如水蒸气、二氧化碳等,当热处理完成,管式炉温度低于100℃时,我们将高纯氮气切换为高纯氧气,一个小时后再取出样品.电化学测试表明,在氧气中暴露了一个小时后,0.88PpPD/CB样品的氧还原活性极大地降低了,而且X射线光电子能谱表明其氧含量提高了一倍,接近12%.因此,我们证实了氧气会和0.88PpPD/CB样品反应,导致样品的氧还原活性降低.所以,对于未来掺氮碳材料的大规模应用,要考虑其在空气中的稳定性,以及如何避免和氧气接触.

关键词: 苯二胺, 炭黑, 复合结构, 氧气还原反应, 稳定性

Abstract:

Nitrogen-doped carbon materials exhibiting high oxygen reduction reaction activity were prepared via the pyrolysis of a poly-p-phenylenediamine/carbon black composite. The as-synthesized catalyst showed excellent catalytic activity in alkaline solution, and outperformed commercial Pt/C in KOH solution (0.1 mol/L), as demonstrated by the higher current density and the more positive half-wave potential. Scanning electron microscopy and N2 adsorption-desorption analyses indicated that a composite structure, in which the N-rich surface of the poly-p-phenylenediamine had an increased active center concentration and the high external surface area of the carbon black was conducive to the mass transport, is highly beneficial in terms of promoting the oxygen reduction reaction. However, the activity of this catalyst underwent an obvious decrease following exposure to air for 30 d. X-ray photoelectron spectroscopy showed that the oxygen content in the catalyst was increased by prolonged air exposure. O 1s spectrum showed increases in the C=O and C-O components, suggesting that atmospheric oxygen reacted with the catalyst. This oxidation leaded to the deactivation of active center, thus the catalytic activity decreased. Based on these results, the stability in air of nitrogen-doped carbon materials must be taken into consideration when assessing applications as alternatives to platinum-based materials.

Key words: Phenylenediamine, Carbon black, Composite structure, Oxygen reduction reaction, Durability