全站搜索
当前日期时间
当前时间:
当石墨烯“牵手”碳纳米管--新型高效双功能氧还原-氧析出催化剂的制备和性能
清华大学绿色反应工程与工艺北京市重点实验室    2014-08-21 16:48:56   

当石墨“牵手”碳纳米管

--新型高效双功能氧还原-氧析出催化剂的制备和性能

随着化石能源的日益枯竭和随之而来的环境恶化日益严峻,新型、高效的可再生能源系统是当今社会广为关注的焦点。在能源转化过程中,氧-氧活化,即氧还原和氧析出是重要的化学反应。以氧-氧活化反应为核心可以构建燃料电池、金属空气电池和水分解等新型能源体系,具有广泛的应用前景。然而,氧还原和氧析出两个反应动力学往往进行缓慢,需要较大的过电势作为驱动,降低了能量利用效率。发展兼具氧还原和氧析出两个反应的高电催化活性的催化剂是实现氧-氧活化参与能源体系的有效可持续利用的重要手段。基于铂、铱、钌等贵金属及其合金或氧化物的催化剂虽然催化活性较高,但其面临价格昂贵、资源稀缺、稳定性差等问题,严重制约其广泛应用。如果能够开发价格低廉、丰富易得、性能优异的非贵金属和非金属催化剂,则有望高效提高该过程的效率。

以石墨烯和碳纳米管为代表的新型纳米材料在催化剂应用领域具有广阔的应用前景。通过对其进行氮原子等的掺杂可以有效调控其导电性和催化反应活性。近日,清华大学的张强、魏飞教授研究组和新加坡南洋理工大学的于丁山博士合作研究设计出一种基于氮掺杂的石墨烯/碳纳米管杂化物的新型高效双功能氧还原-氧析出催化剂,相关文章在2014年6月11日出版的Small发表期刊的Graphene Research in China特刊中发表,文中图片被选为该期期刊的封面

该课题组综合了石墨烯和碳纳米管的双重优良特性,利用一种能同时催化两种材料生长的催化剂(层状双羟基复合金属氢氧化物,即水滑石),通过化学气相沉积一步制备出共价连接的氮掺杂石墨烯/单壁碳纳米管的杂化物。单一组分的石墨或者碳纳米管往往因为其石墨层间的范德瓦尔斯作用力而堆叠或者缠结,而杂化之后的纳米结构就具有自分散的特性,有效抑制团聚问题。这种杂化材料具有高比表面积(812.9 m2/g)、丰富的孔结构(2.233 cm3/g),高活性位点以及高的导电性(53.8 S/cm),从而其具有优良的电催化活性。将其用于氧还原反应,发现这种杂化材料具有接近于商用Pt/C的催化活性,同时其稳定性和对甲醇的耐受性都要优于商用Pt/C催化剂。另外,此种氮掺杂的石墨烯/碳纳米管杂化物材料对氧析出反应也具有很好的催化活性。该种杂化物材料其原料廉价易得、制备方法简单易于批量生产,同时其催化活性高、稳定性好。因此,这种氮掺杂的石墨烯/碳纳米管杂化物材料有望取代贵金属催化剂,为燃料电池、金属空气电池和水分解等能源体系的进一步发展带来新的契机。

 

 

 

Rational hybridization of N-doped graphene/carbon nanotube for oxygen reduction and oxygen evolution reaction

 

       Scientists at Tsinghua University, China, and Nanyang Technological University, Singapore, have designed an intrinsic-disperse nanocarbon architecture hybridizing N-doped graphene and SWCNTs, which can serve as a superior bifunctional electrocatalyst for both oxygen reduction and evolution reactions.

 

       Nowadays, renewable and high-capacity energy systems like fuel cells and metal-air batteries are highly desired to sustainable fuel the society. “As the key electrode reactions for such energy systems, ORR and OER, short for oxygen reduction and oxygen evolution reaction, are multi-electron process and kinetically sluggish. Consequently, high efficient electrocatalysts for these reactions are needed to boost the reaction rate”, said Dr. Qiang Zhang, an associate professor at Department of Chemical Engineering, Tsinghua University. “In spite of high catalytic activity, the conventional noble metal catalysts like Pt, Ru, and Ir, are suffered from the high cost and poor stability. As a result, scientists are seeking for substitute catalysts from non-noble metal and even non-metal materials. Heteroatoms doped nanocarbon materials afford much improved reactivity and catalytic performance. Our group explored the in situ growth of N-doped graphene and SWCNT hybrids and their superior electrocatalytic performance for ORR and OER.”

 

       “The layered double hydroxides were employed as the bifunctional catalyst for the simultaneous growth of graphene and SWCNTs, forming the three dimensional interconnected network”, Prof. Fei Wei told Phys.Org.

 

       Actually, Zhang’s group have done a lot of research on the synthesis of hierarchical nanocarbon materials with the layered double hydroxides as the catalysts and achieved great progress with many excellent papers published. “As for the two typical nanocarbon materials, 1D CNTs and 2D graphene nanosheets, both of them are inclined to aggregate or stack with each other due to the strong van der Waals forces. That hinders the full utilization of the active sites for catalytic reactions. In fact, the integration of graphene and CNTs into a hybrid material is quite a promising strategy to enhance the dispersion of graphene and CNTs, to inherit the advantages of both graphene and CNTs, and to obtain an efficient and effective electronic and thermal conductive 3D network”, Qiang said. “The FeMoMgAl LDHs derived bifunctional catalysts embedded with thermally stable Fe NPs not only served as an efficient catalyst for the growth of N-doped SWCNTs, but also supplied a lamellar substrate for the templated deposition of N-doped graphene. Therefore, the simultaneous growth of N-doped graphene and SWCNTs can be achieved with the covalent C-C bonding connection.”

 

       Based on this concept, Gui-Li Tian, a graduate student and the first author, developed an in-situ chemical vapor deposition strategy for the graphene/SWCNT hybrid synthesis. “N-doped Graphene and SWCNTs are intrinsically dispersed in this novel carbon architecture and the N-containing functional groups well dispersed in the conductive scaffold. The as-fabricated hybrids are with a large surface area, high porosity and also high graphitic degree. All these characters render the N-doped graphene/SWCNT hybrids with a high ORR activity, much superior to two constituent components and even comparable to the commercial 20 wt% Pt/C catalysts with much better durability and resistance to crossover effect”, said Gui-Li. What’s more, they demonstrated that such novel carbon architecture is also electrocatalytically active for OER. “This indicated that the hybrid material is a promising bifunctional electrocatalyst for the regenerative fuel cells and rechargeable metal-air batteries involving oxygen electrochemistry.” said Dr. Dingshan Yu at Nanyang Technological University, Singapore.

 

       “We foresee that compared with random graphene and CNTs, more potential applications may arise if the enhanced electrical and optical properties of doped graphene/CNT hybrids were fully exploited”, said Qiang. Additionally, this work also provides a structural platform toward the design of 3D interconnect materials with extraordinary electron pathways as well as tunable surface/interface that can be used in areas, such as catalysis, separation, drug delivery, energy conversion and storage.

 

 

论文链接:

Tian GL, Zhao MQ, Yu DS, Kong XY, Huang JQ, Zhang Q, Wei F. Nitrogen-Doped Graphene/Carbon Nanotube Hybrids: In-Situ Formation on Bifunctional Catalysts and Their Superior Electrocatalytic Activity for Oxygen Reduction Reaction. Small 2014. 10(11), 2251-2259. doi:10.1002/ smll.201303715.

http://onlinelibrary.wiley.com/doi/10.1002/smll.201303715/abstract

新闻链接:

http://www.materialsviewschina.com/2014/06/dang-shi-mo-xi-qian-shou-tan-na-mi-guan/

浏览 (70) | 评论 (0) | 评分(0) | 支持(0) | 反对(0) | 发布人:管理员
将本文加入收藏夹
联系我们




◇电话:010-62796110

◇传真:010-62772051

◇邮编:100084

 
 
版权所有 Copyright(C)绿色反应工程与工艺北京市重点实验室
访问统计