单原子Fe-Nx团簇掺杂多孔碳纳米管的可控制备与氧还原性能研究

Carbon nanotubes (CNTs) have large aspect ratio, functionalizable outer carbon layer for active site loading and highly crystallized inner wall for efficient electron transport. Therefore, CNTs are expected to play an important role in catalyzing the oxygen reduction reaction (ORR). However, the ORR catalysis performance of conventional CNTs is unsatisfactory, because of the low concentration of active catalytic sites and the lack of micropores that make electrolyte accessible to the active sites. To address these problems, here we propose to develop a simple and scalable volatile atom isolation method to prepare a porous CNT doped with a high concentration and uniformly distributed N-coordinated single atom Fe-Nx clusters. Briefly, CNTs with selectively functionalized outer surface are loaded with N-containing precursor, followed by Fe/Zn ions adsorption on negatively-charged N functional group, and finally one-step pyrolysis. During the pyrolysis, Fe atoms are uniformly dispersed and spatially isolated by Zn atoms and convert into N-coordinated single atom Fe clusters directly. Furthermore, micropores are formed along with the volatilization of the Zn atoms, which can fully expose the active sites. The effects of Zn ion concentration, N-containing precursor type, and carbonization conditions on the pore structure, the content and distribution of Fe-Nx active sites will be investigated. We will study the catalytic mechanism of Fe-Nx active site toward ORR and the influence of CNT structure on the ORR catalysis performance. The relationship between the atomic composition, surface morphology of the catalyst and its ORR catalysis performance will be elucidated. The low cost, high performance N-coordinated single atom Fe cluster doped CNT ORR catalysts obtained will pave the way for their use in fuel cells.

碳纳米管（CNT）具有大长径比，外碳层可官能化承载活性位点、内碳层可高效传输电子等特点，可望用作高效氧还原（ORR）电催化材料。但普通CNT的催化活性位点少，且缺少使活性位点与电解液充分接触的孔结构，因此其ORR活性不高。本申请提出采用“挥发隔离原子”方法，设计制备高浓度、单原子Fe-Nx团簇掺杂多孔CNT，并将其用于ORR催化。即在CNT表面担载含氮有机物，带负电的含氮基团吸附Fe/Zn离子，经高温碳化形成高浓度、均匀的单原子Fe-Nx团簇活性位，同时Zn挥发留下微孔使活性位充分暴露。研究Zn离子浓度、含氮有机物种类、碳化条件等对材料孔隙、单原子Fe-Nx团簇浓度和分布的影响。分析Fe-Nx团簇催化ORR过程，理解CNT多孔结构影响ORR性能的机制，阐释其构效关系。获得超高活性单原子Fe-Nx团簇掺杂多孔CNT催化材料，为高性能、低成本氧还原催化剂在燃料电池等领域的应用奠定科学基础。

碳纳米管（CNT）具有大长径比，外碳层可官能化承载活性位点、内碳层可高效传输电子等特点，可望用作高效氧还原（ORR）电催化材料。但普通CNT的催化活性位点少，且缺少使活性位点与电解液充分接触的孔结构，因此其ORR活性不高。在国家自然科学基金委面上项目资助下，本项目建立了倆种单原子Fe-Nx 团簇掺杂多孔碳纳米管的可控制备方法，并研究了其ORR催化活性及机理。为了推进单壁碳纳米管（SWCNT）柔性薄膜在电催化一体化薄膜电极方面的应用潜力，着重研究全气相法在SWCNT薄膜上引入活性位点关键技术，分析Fe-Nx团簇催化ORR过程，理解CNT多孔结构影响ORR性能的机制，阐释其构效关系。项目执行期间，取得的重要研究成果有：1）发展了氟化抓取Fe单原子、氨化锚定Fe-Nx活性位点的气相处理新技术，将SWCNT薄膜上的Fe催化剂颗粒杂质变废为宝，即保持了SWCNT薄膜的宏观结构，又引入了丰富的Fe-Nx高活性位点；2）研究了单原子Fe-Nx 团簇均匀掺杂多孔碳纳米管（SAFe-SWCNT）薄膜的氧还原性能，在-3 mA/cm2的电流密度下，碳纳米管薄膜的氧还原电位比常用贵金属Pt/C催化剂负载在玻碳电极上高41 mV；以SAFe-SWCNT薄膜为电催化薄膜电极，分别构建了锌空电池和柔性全固态锌空电池，获得了优异的性能；3）采用密度泛函理论（DFT）计算结合催化动力学实验，研究了Fe-Nx团簇催化ORR过程及构效关系，阐明了SAFe-SWCNT薄膜优异电催化性能的机制；4）开展了Ni基单壁碳纳米管薄膜电催化电极的控制制备与性能研究。上述成果为高性能、低成本氧还原催化剂在燃料电池等领域的应用奠定科学基础。项目组成员在Applied Catalysis B-Environmental、Advanced Science、Carbon等高水平杂志上发表相关SCI 论文6篇，申请发明专利2项，在国内外学术会议作邀请/口头/展板报告4次。