原子尺度非贵金属氧还原电催化剂的可控构筑及催化机理研究

The high-cost and low stability of cathode catalysts have been the main bottleneck that blocks the practical application of proton exchange membrane fuel cell (PEMFC). Atomically dispersed non-noble metal-nitrogen-carbon (M-N-C) catalysts are regarding as the most promising advanced materials to replace noble metal catalysts , owing to their excellent activity, good durability and low cost. However, the traditional synthesis methods for single-atom catalysts are not easy to control, increasing the metal content will lead to atoms aggregation, reducing the active sites. In order to solve these problems, the solvothermal and solid phase reactions will be simultaneously employed in this project. Based on the coordination interaction between pyridinic-N groups and metal ions, the ordered and alternate distribution of active sites at atom level will be generated in catalyst precursor. By introducing zinc as an isolation agent to hinder the aggregation of single atoms, the number of single-atom sites and catalyst activity are improved. Synchrotron radiation technology will be used to reveal the relationship between the fine structure of active sites and the oxygen reduction activity of the catalyst. Combining with density functional theory calculations, the electron-proton coupling process and the control steps of oxygen reduction will be studied and the oxygen reduction mechanism will be explored. The research in this project can provide highly efficient and low-cost catalysts for PEMFC cathode, new idea for the design and synthesis of single-atom catalysts and guidance for the development of small molecular oxygen electro-reduction theory. Therefore, it has important scientific significance.

阴极催化剂成本和稳定性已成为制约质子交换膜燃料电池实用化的主要瓶颈。原子级分散的非贵金属-氮-碳（M-N-C）催化剂表现出优良的活性、稳定性和较低的成本，有望成为取代贵金属催化剂的先进材料。然而传统的合成单原子方法不易控制，增加金属含量会导致原子团聚，催化剂活性位点减少。为此，本项目拟采用液相与固相合成相结合的方法，基于吡啶N与金属离子的配位作用，在分子水平上构建单个活性位点有序、交替分布的催化剂前驱体；引入锌作为隔离剂，阻止单原子团聚，提高活性位点数量和氧还原活性。采用同步辐射揭示催化剂活性位点精细结构与催化剂氧还原活性之间的关系，并结合密度泛函理论计算，研究氧分子的电子-质子耦合过程，确认氧还原过程的控制步骤，探寻氧还原机理和作用机制。本项目可为燃料电池阴极提供高效低成本的催化剂，为单原子催化剂设计合成提供新思路，同时也可为小分子氧的电还原理论发展提供指导，具有重要的科学意义。

本项目通过对原子级分散位点的金属-氮-碳催化剂的理性设计和精细调控，发展了面向燃料电池的非贵金属单原子催化剂宏量合成方法学，丰富氧还原催化剂的种类。应用自上而下的气相转运合成策略实现了配位结构均匀的单原子催化剂的可控制备，实现了对活性中心金属-金属键、配位数等原子结构的精准调控。相比于商业的Pt/C催化剂，具有更低的成本，更高的活性和稳定性。采用分子筛为硬模板剂，通过孔道自组装的方式，缩短离子扩散和电子传导距离，提升单原子材料的氧还原催化活性，并进一步深入研究了形成机理。利用有机小分子隔离剂一步热解还原，限制金属颗粒或团簇的形成，实现高载量和高热稳定性的多种单原子催化剂合成，奠定了催化剂大规模制备技术基础。通过研究在氧还原过程中催化剂的表面组成、形貌、化学结构和电子结构以及催化剂表面的吸附和反应性能，并结合理论计算，掌握了氧气分子在单原子活性位点上的反应机制和反应路径，进一步获得催化剂结构、活性位点与电催化反应机理之间的关系。最后基于对催化体系的深入理解和模型构建来进行高通量催化剂筛选；优化了燃料电池的组装技术，将获得的高性能催化剂组装成燃料电池器件，加快从材料合成到实用化进程。