Maldonado Stephen, Stevenson Keith J
Department of Chemistry and Biochemistry, Center for Nano- and Molecular Science and Technology, Texas Materials Institute, The University of Texas at Austin, Austin, Texas 78712, USA.
J Phys Chem B. 2005 Mar 17;109(10):4707-16. doi: 10.1021/jp044442z.
Nondoped and nitrogen-doped (N-doped) carbon nanofiber (CNF) electrodes were prepared via a floating catalyst chemical vapor deposition (CVD) method using precursors consisting of ferrocene and either xylene or pyridine to control the nitrogen content. Structural and compositional differences between the nondoped and N-doped varieties were assessed using TEM, BET, Raman, TGA, and XPS. Electrochemical methods were used to study the influence of nitrogen doping on the oxygen reduction reaction (ORR). The N-doped CNF electrodes demonstrate significant catalytic activity toward oxygen reduction in aqueous KNO(3) solutions at neutral to basic pH. Electrochemical data are presented which indicate that the ORR proceeds by the peroxide pathway via two successive two-electron reductions. However, for N-doped CNF electrodes, the reduction process can be treated as a catalytic regenerative process where the intermediate hydroperoxide (HO(2)(-)) is chemically decomposed to regenerate oxygen, 2HO(2)(-) <==> O(2) + 2OH(-). The proposed electrocatalysis mechanisms for ORR at both nondoped and N-doped varieties are supported by electrochemical simulations and by measured difference in hydroperoxide decomposition rate constants. Remarkably, approximately 100 fold enhancement for hydroperoxide decomposition is observed for N-doped CNFs, with rates comparable to the best known peroxide decomposition catalysts. Collectively the data indicate that exposed edge plane defects and nitrogen doping are important factors for influencing adsorption of reactive intermediates (i.e., superoxide, hydroperoxide) and for enhancing electrocatalysis for the ORR at nanostructured carbon electrodes.
通过浮动催化剂化学气相沉积（CVD）法，使用由二茂铁和二甲苯或吡啶组成的前驱体来控制氮含量，制备了非掺杂和氮掺杂（N掺杂）的碳纳米纤维（CNF）电极。使用透射电子显微镜（TEM）、比表面积分析仪（BET）、拉曼光谱仪、热重分析仪（TGA）和X射线光电子能谱仪（XPS）评估了非掺杂和N掺杂品种之间的结构和成分差异。采用电化学方法研究了氮掺杂对氧还原反应（ORR）的影响。N掺杂的CNF电极在中性至碱性pH的硝酸钾（KNO₃）水溶液中对氧还原表现出显著的催化活性。给出的电化学数据表明，ORR通过过氧化物途径经两个连续的两电子还原进行。然而，对于N掺杂的CNF电极，还原过程可视为催化再生过程，其中中间产物过氧化氢根（HO₂⁻）化学分解以再生氧气，2HO₂⁻⇌O₂ + 2OH⁻。电化学模拟以及测量得到的过氧化氢分解速率常数差异支持了所提出的非掺杂和N掺杂品种上ORR的电催化机制。值得注意的是，观察到N掺杂的CNF对过氧化氢分解有大约100倍的增强，其速率与最知名的过氧化物分解催化剂相当。总体而言，数据表明暴露的边缘平面缺陷和氮掺杂是影响活性中间体（即超氧根、过氧化氢根）吸附以及增强纳米结构碳电极上ORR电催化的重要因素。
