催化学报 ›› 2016, Vol. 37 ›› Issue (8): 1275-1282.DOI: 10.1016/S1872-2067(15)61123-8

• 论文 • 上一篇    下一篇

氮掺杂纳米碳块的制备及氧还原的高电化学催化活性

张亭亭, 何传生, 黎琳波, 林雨青   

  1. 首都师范大学化学系, 北京 100048
  • 收稿日期:2016-01-04 修回日期:2016-04-29 出版日期:2016-07-29 发布日期:2016-08-01
  • 通讯作者: Yuqing Lin
  • 基金资助:

    国家自然基金(21375088,21575090);北京市教育委员会科研计划(KM201410028006);北京市市属高校青年拔尖人才项目(CIT&TCD201504072);北京市教育委员会基础科学发展计划.

Preparation of nitrogen-doped carbon nanoblocks with high electrocatalytic activity for oxygen reduction reaction in alkaline solution

Tingting Zhang, Chuansheng He, Linbo Li, Yuqing Lin   

  1. Department of Chemistry, Capital Normal University, Beijing 100048, China
  • Received:2016-01-04 Revised:2016-04-29 Online:2016-07-29 Published:2016-08-01
  • Contact: Yuqing Lin
  • Supported by:

    This work was supported by the National Natural Science Foundation of China (21375088, 21575090), Scientific Research Project of Beijing Educational Committee (KM201410028006), Youth Talent Project of the Beijing Municipal Commission of Education (CIT&TCD201504072), and Scientific Research Base Development Program of the Beijing Municipal Commission of Education.

摘要:

面对全球化的能源危机,燃料电池由于其高效性和可重复使用性成为越来越具有潜力的能量转化设备.阴极发生的氧气还原反应对于燃料电池的性能十分重要,寻找高效的氧还原催化剂在很大程度上可以提高燃料电池的性能.传统的氧还原催化剂是贵金属铂,但是铂的价格十分高,较差的稳定性和选择性限制了它的商业化应用,因此找到一种廉价高效的非贵金属氧还原催化剂来代替铂基催化剂成为目前的研究热点.我们最近发现将纯的三羟甲基氨基甲烷置于管式炉中在800℃下真空烧制2h,可以简单快捷地得到一种含N量为4.11%的纳米碳块(标记为NCNBs-800),该材料可用于催化电化学氧气还原反应.同样情况下在700和900℃下合成的材料标记为NCNBs-700和NCNBs-900. 采用傅里叶变换红外光谱(FTIR)、X射线光电子能谱(XPS)、扫描电子显微镜(SEM)、X射线衍射(XRD)和电化学旋转圆盘方法与技术对催化剂的成分、形貌和电催化性能进行了表征.SEM表明NCNBs-800为直径为60nm的碳块,用FTIR手段表征了NCNBs-800的结构变化,三羟甲基氨基甲烷中的-OH和-NH2在高温下发生消去反应,形成了饱和度不同的C-N键和C-C键.这些饱和度不同的N原子和C原子增加了材料的缺陷结构和活性位点,进一步促进了氧还原反应的催化性能.采用XPS分析了NCNBs-800表面的元素,通过对N1s进行分峰拟合,发现NCNBs-800含有能促进氧还原性能的吡啶-N和吡咯-N,特别是吡啶-N,它吸电子的能力很强,从而导致与它邻近的C原子表面具有一定的正电荷,这些正电荷促进了氧气的吸附和还原,为氧气还原反应提供活性位点,促进氧气还原反应的发生.XRD结果表明,三羟甲基氨基甲烷热解前后的XRD谱图有明显变化,热解后的三羟甲基氨基甲烷呈现两个宽峰,代表着杂化碳的存在.NCNBs-800的衍射峰强度比NCNBs-700以及NCNBs-900大,但是宽度则比NCNBs-700以及NCNBs-900小,这表明800℃有利于材料的石墨烯化及碳化过程.电化学阻抗可以表明修饰电极的表面性质,阻抗图中高频处半圆的直径大小代表电子转移阻力,低频处的线性部分代表扩散过程. 阻抗数据表明,NCNBs-800的电荷转移电阻可与Pt/C催化剂相比,但是比裸露的玻碳电极小.这表明NCNBs-800有较好的导电性和电化学性质.CV曲线表明NCNBs-800氧还原的起始电位是 -0.05V(vs Ag/AgCl),氧气的还原电位是0.20V(vs Ag/AgCl),说明NCNBs-800具有良好的电化学催化性能.旋转环盘电极仪测得的氧还原极化曲线表明,在-0.3 to -0.8V下的NCNBs-800氧还原的电子转移数为3.4,过氧化氢产率为52%-35%,表明NCNBs-800呈现一个提高的四电子过程.稳定性对于燃料电池氧气还原反应也是一个十分重要的性能,通过计时电流技术在电压为-0.2V下对NCNBs-800与Pt/C进行了稳定性测试. 结果表明,在2500s之后NCNBs-800相对于它的最初催化活性损失为17.56%,而Pt/C损失了30.71%,从而说明NCNBs-800的稳定性优于Pt/C.总之,我们通过一步热解的简易技术制备了一种氮掺杂纳米碳材料,该碳材料具有廉价、高效和容易制备等特点,具有良好的电化学催化性能,有望在燃料电池氧化还原反应中得到大规模应用.

关键词: 氮掺杂纳米碳块, 三羟甲基氨基甲烷, 电化学催化剂, 氧气还原反应, 纳米催化剂

Abstract:

The oxygen reduction reaction (ORR) is traditionally performed using noble-metals catalysts, e.g. Pt. However, these metal-based catalysts have the drawbacks of high costs, low selectivity, poor stabilities, and detrimental environmental effects. Here, we describe metal-free nitrogen-doped carbon nanoblocks (NCNBs) with high nitrogen contents (4.11%), which have good electrocatalytic properties for ORRs. This material was fabricated using a scalable, one-step process involving the pyrolysis of tris(hydroxymethyl)aminomethane (Tris) at 800 ℃. Rotating ring disk electrode measurements show that the NCNBs give a high electrocatalytic performance and have good stability in ORRs. The onset potential of the catalyst for the ORR is -0.05 V (vs Ag/AgCl), the ORR reduction peak potential is -0.20 V (vs Ag/AgCl), and the electron transfer number is 3.4. The NCNBs showed pronounced electrocatalytic activity, improved long-term stability, and better tolerance of the methanol crossover effect compared with a commercial 20 wt% Pt/C catalyst. The composition and structure of, and nitrogen species in, the NCNBs were investigated using Fourier-transform infrared spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The pyrolysis of Tris at high temperature increases the number of active nitrogen sites, especially pyridinic nitrogen, which creates a net positive charge on adjacent carbon atoms, and the high positive charge promotes oxygen adsorption and reduction. The results show that NCNBs prepared by pyrolysis of Tris as nitrogen and carbon sources are a promising ORR catalyst for fuel cells.

Key words: Nitrogen-doped carbon nanoblock, Trihydroxymethyl aminomethane, Electrocatalyst, Oxygen reduction reaction, Nanocatalyst