Thermo-stability and active site structure of Fe/N/C electrocatalyst for oxygen reduction reaction
- 2017年第23卷 
研制高活性的Fe/N/C氧还原催化剂对于降低燃料电池成本、实现商业化应用有重要意义. 为了实现Fe/N/C催化剂的理性设计，需要深入研究其活性位结构. 本文我们发展一种研究活性位结构的新策略，即以预先合成好的聚间苯二胺基Fe/N/C催化剂(PmPDA-FeNx/C)为起始物，对其在1000~1500 oC高温下再次进行热处理并使其失活，通过关联催化剂热处理前后的结构变化与氧还原催化性能来揭示活性位结构. 实验结果表明，随着热处理温度升高，活性中心结构被破坏，铁原子析出团聚并形成纳米颗粒，氮元素挥发损失，导致催化剂失活. XPS分析显示，低结合能含氮物种的含量与催化剂的ORR活性呈良好的正相关性，表明活性中心很可能是由吡啶N和Fe-N物种构成的.The development of Fe/N/C electrocatalyst for oxygen reduction reaction (ORR) is vital for the large-scale applications of proton exchange membrane fuel cells. Understanding the active site structure will contribute to the rational design of highly active catalysts. In this study, the as-prepared Fe/N/C catalyst based on poly-m-phenylenediamine (PmPDA-FeNx/C) catalyst with the high ORR activity was subjected to the high-temperature heat treatment again at 1000 ~1500 oC. The degradation of in the ORR activity of PmPDA-FeNx/C by with various heat treatments was correlated to the change of elemental compositions, chemical states and textural properties. As the temperature elevated, the Fe atoms aggregated to form nanoparticles, while the gaseous N-containing species volatilized and the amount of N contents decreased, resulting in the destruction of active sites. The XPS analysis revealed that the content of N species with low binding energy show good positive correlation with the ORR kinetic current of catalyst, demonstrating that the pyridinic N and Fe-N species are probably main components of active sites and contribute to the high ORR activity. This study provides a new strategy to investigate the nature of active centre.