氮掺杂石墨烯的制备及其对氧还原反应的电催化性能

以氧化石墨烯（GO）为原料、丙酮肟（DMKO）为还原剂和氮掺杂剂，采用化学还原法制备了不同氮掺杂含量的石墨烯（NG）. 利用场发射透射电子显微镜（FETEM）、紫外-可见（UV-Vis）光谱、傅里叶变换红外（FTIR）光谱、X射线光电子能谱（XPS）、zeta 电位和纳米粒度分析、循环伏安（CV）和旋转圆盘电极（RDE）等手段对材料的形貌、结构、成分和电化学性质进行表征. 结果显示：DMKO能有效地还原GO，且通过调节GO与DMKO的质量比，可以得到不同还原效果的NG，其氮含量范围为4.40%-5.89%（原子分数）；GO与DMKO的质量比为1：0.7时制备的氮掺杂石墨烯（NG-1）在O₂饱和0.1 mol·L^-1 KOH溶液中对氧还原反应（ORR）的电催化性能最佳，其ORR峰电流为0.93 mA·cm^-2，电子转移数为3.6，这归因于其较高含量的吡啶-N增加了材料的ORR活性位点. 此外，石墨化-N由于其较高的电子导电性倾向于产生较高的氧还原峰电流，而吡啶-N较低的超电势倾向于产生较正的氧还原峰电位. 与商用Pt/C相比，该材料展现出了优异的抗CH₃OH“跨界效应”的特性.

Preparation of Nitrogen-Doped Graphene and Its Electrocatalytic Activity for Oxygen Reduction Reaction

Nitrogen-doped graphene (NG) was prepared by chemical reduction of graphene oxide (GO) using dimethyl ketoxime (DMKO) as reducing and doping agents. The morphologies, structures, compositions, and electrocatalytic activities of the as-prepared materials were investigated using field-emission transmission electron microscopy (FETEM), ultraviolet- visible (UV-Vis) spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), zeta potential and nanoparticle analyses, cyclic voltammetry (CV), and the rotating disk electrode (RDE) method. The results showed that GO sheets were effectively reduced by DMKO. NG samples with different nitrogen contents were obtained by adjusting the mass ratio of GO to DMKO; the nitrogen contents were in the range 4.40%-5.89% (atomic fraction). NG-1, obtained using a GO/DMKO mass ratio of 1:0.7, showed excellent electrocatalytic activity in the oxygen reduction reaction (ORR) in an O₂-saturated 0.1 mol·L^-1 KOH solution. The peak current was 0.93 mA·cm^-2, and the number of electrons transferred per O₂ was 3.6; this was attributed to the increase in the number of ORR active sites in the presence of pyridinic-N. In addition, the electrocatalytic activity of NG was found to be dependent on the graphitic-N content, which determined the limiting current density, because of its higher electronic conductivity. The pyridinic-N content improved the onset potential, because of its lower overpotential for the ORR. NG therefore exhibited a high selectivity in the ORR, with good tolerance of methanol cross-over effects. It is therefore superior to commercial Pt/C catalysts.