宏量可控构筑原子尺度非贵金属氧还原催化剂及催化机理研究

The high-cost and low activity of cathode catalysts have been the main bottleneck that blocks the practical application of proton exchange membrane fuel cells (PEMFCs). Atomically dispersed non-noble metal-nitrogen-carbon (M-N-C) catalysts endow high activity for ORR and low cost. However, the traditional synthesis methods for single-atom catalysts are sensitive for synthesis conditions and not easy to control. Namely, increasing the production of single atom catalysts may lead to atomic agglomeration and thus reduce the active site of catalysts, which is disadvantageous for its practical applications. To this end, this project selects non-precious metal or alloys as metal source based on the high temperature gas migration synthesis. Specifically, we will design precisely surface atomic coordination structure and composition for optimizing the activity and stability of non-precious single metal atom catalysts and realizing the large-scale production of single atom catalysts with high performance. Combining synchrotron radiation technique with density functional theory calculations, we will construct the relationship between the metal atomic coordination structure and oxygen electro-reduction process. 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, as well as the guidance for the development of small molecular oxygen electro-reduction theory. Therefore, it has important scientific significance.

阴极催化剂成本和活性已成为制约质子交换膜燃料电池实用化的主要瓶颈。非贵金属单原子氧还原催化剂（M-N-C）具有优良的氧还原活性和较低的成本，有望取代贵金属催化剂。然而传统合成单原子催化剂的方法对反应条件敏感，扩大生产易导致原子团聚，催化剂活性位点减少，不利于单原子催化剂的实用化。为此，本项目选取非贵金属单质或合金为金属源，以高温气相迁移合成为基础，通过表面原子配位结构和组分的精准设计，调控金属活性中心的配位环境，优化非贵金属单原子催化剂活性和稳定性，实现高性能单原子催化剂的宏量制备。结合同步辐射与理论计算揭示表面单原子配位结构与氧气分子电还原过程之间的作用机制。本项目可为燃料电池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，同时也可为氧气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。采用固相合成方法，通过精准控制原子尺度界面结构，降低氧还原反应能垒，提升氧还原催化活性，并进一步深入研究了形成机理。利用离子交换热解还原，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。