School of Materials Science and Engineering, University of Shanghai for Science and Technology, 516 Jungong Road, Shanghai 200093, P. R. China.
State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi Road, Shanghai 200050, P. R. China.
Nanoscale. 2016 Oct 27;8(42):18134-18142. doi: 10.1039/c6nr06716f.
In situ formation of nitrogen-doped carbon nanoparticles on hollow carbon spheres (NHCSs) were successfully realised via a simple, scalable emulsion polymerization route using melamine as the nitrogen precursor, followed by thermal treatment at 1000 °C in N. All NHCSs show large BET specific surface areas (648.2-837.7 cm g) and pore volumes (0.91-1.16 cm g), evidently superior to N-free hollow carbon spheres (HCSs) (524.3 cm g and 0.48 cm g, respectively). This unique nanocomposite has hierarchical micro-/mesoporosity (1.9 nm and 16.2-19.0 nm). The X-ray photoelectron spectroscopy (XPS) measurements indicate the successful introduction of N atoms into the carbon framework and that the N-doping level can be controlled by changing the amount of melamine. The N-doping by adding melamine during the hydrothermal process not only affects the morphologies and porosities of the final samples, but also improves the electrocatalytic activity compared to N-free HCSs. NHCS-2, prepared with the molar melamine/hexamethylentetramine ratio of 1, showed the best electrocatalytic activity for the oxygen reduction reaction (ORR) in terms of onset potential, half-wave potential and limit current density. The NHCS-2 exhibited not only excellent activity with a mainly four-electron reaction pathway, but also superior long-term durability and methanol tolerance to that of commercial Pt/C in alkaline solution. The excellent electrocatalytic activity of the NHCS-2 is mainly due to its high relative content of pyridinic- and graphitic-N groups as well as unique hierarchical micro-/mesoporosity and a large specific surface area, advantageous for mass transfer and thus improving the electrocatalytic activity.
通过使用三聚氰胺作为氮前体的简单、可扩展的乳液聚合路线，成功地在空心碳球 (NHCSs) 上原位形成了氮掺杂碳纳米粒子，然后在 N 中于 1000°C 进行热处理。所有 NHCSs 都表现出大的 BET 比表面积（648.2-837.7 cm g）和孔体积（0.91-1.16 cm g），明显优于无氮空心碳球（HCSs）（分别为 524.3 cm g 和 0.48 cm g）。这种独特的纳米复合材料具有分级的微孔/介孔（1.9nm 和 16.2-19.0nm）。X 射线光电子能谱（XPS）测量表明成功地将 N 原子引入到碳骨架中，并且可以通过改变三聚氰胺的量来控制 N 掺杂水平。通过在水热过程中添加三聚氰胺进行 N 掺杂不仅会影响最终样品的形态和孔隙率，而且与无氮 HCSs 相比，还会提高电催化活性。以摩尔三聚氰胺/六亚甲基四胺的比例为 1 制备的 NHCS-2 在起始电位、半波电位和极限电流密度方面表现出对氧还原反应（ORR）的最佳电催化活性。NHCS-2 不仅表现出主要的四电子反应途径的优异活性，而且在碱性溶液中还具有出色的长期耐久性和甲醇耐受性，优于商业 Pt/C。NHCS-2 的优异电催化活性主要归因于其高相对含量的吡啶型和石墨型-N 基团以及独特的分级微孔/介孔和大比表面积，有利于传质，从而提高电催化活性。
