过渡金属单原子负载碳纳米片的设计制备及其氧还原机理研究

As the representative of new ORR catalytic materials, atomically dispersed metal anchored carbon with high ORR pefromance, is expected to replace the noble metal Pt, play an important role in the field of fuel cells. Towards the current investigations on relation between the control synthesis,local structure of single atom and the ORR properties lacking of research, the coupling mechanism of multiple factors for oxygen reduction reaction were systematically carried out using atomically dispersed metal anchored carbon as the research object. A new research program of designed synthesis atomically dispersed transition metal anchored on N doped graphene was proposed based on the abundant binding sites and layer structure of g-C3N4. The content and distribution of metal and nitrogen atoms can be controlled by the type and proportion of nitrogen, carbon and metal source materials. The distribution of transition metal atoms and bonding state to nitrogen were systematically studied before and after ORR test, and main factors that affect the stability of transition metal atoms for ORR will be clarified. The inherent relationship between the morphology, performance, bonding state and the ORR catalytic performance will be revealed. This investigation will promote the development of ORR theory and provide new insight into design and fabrication of high efficient ORR catalyst for fuel cells.

以过渡金属单原子负载碳为代表的新型ORR催化材料，有望取代贵金属Pt，在燃料电池领域发挥重要作用。针对目前单原子负载碳材料可控制备、单原子局域结构对性能影响方面缺乏系统研究的现状，本项目以过渡金属单原子负载碳纳米片为研究对象，系统开展多因素作用下ORR催化规律的研究。项目拟利用g-C3N4层状结构及其内部丰富的金属结合位点设计制备过渡金属单原子负载碳纳米片。通过调控氮源、碳源和金属源的种类、比例，配合不同气氛下热处理等条件制备过渡金属单原子分布、掺杂量可控的碳纳米片。采用HAADF-STEM,XANES等技术手段，系统研究单原子局域结构与ORR催化反应的关系，揭示影响过渡金属单原子稳定性的主要因素和相关催化机理。通过本项目研究可以丰富ORR催化剂的制备方法和材料体系，为高效燃料电池催化剂的设计制备提供理论和技术支持。

本项目提出的基于三聚氰胺或双氰胺生成C3N4模板法制备单原子金属负载碳材料方案被成功实施。三聚氰胺纤维吸附过渡金属盐，在高温裂解过程中首先转换为层状C3N4, 不仅为单个Fe原子的分散形式提供了附着点，而且为类石墨烯碳纳米纤维的形成提供了模板，随着进一步升温，原位转换为单原子Fe和B(F)/N共掺杂的类石墨烯碳纳米纤维。由于Fe、B（F）、N共掺杂增加了活性中心，B或者电负性强的F原子的引入进一步改善了电子结构，优化的单原子Fe和B(F)/N共掺杂的类石墨烯碳纳米纤维催化剂表现出比Pt/C催化剂更好的ORR催化活性。利用单原子Fe-B-N掺杂类石墨烯纳米纤维为催化剂组装锌空电池结果证明了所制备锌空电池具有优异的性能和稳定性，证明了所制备的催化剂具有优异的氧还原性能。这项工作不仅为单原子分散多元素掺杂ORR催化剂的设计提供了一种新方法，也为新型燃料电池的开发提供了一种新思路。