类卟啉结构金属单原子内嵌石墨烯的CO2电化学还原反应机理研究及性能优化

The design and synthesis of single metal atom catalysts has maximized the utilization of metal catalysts and greatly promoted the development of high-performance catalysts. Porphyrin-like single metal atom structures embedded in graphene (MNx-G) has showed a good electrochemical stability under the operation conditions for CO2 electrochemical reduction, but the application of MNx-G has been restricted by its poor catalytic activity and insufficient selectivity. How to improve the catalytic activity of MNx-G is an important scientific researching problem for the study of electrocatalytic CO2 reduction. In this project, the free energy changes and transition state barriers of each elementary step for electrochemical reduction of CO2 on MN4-G catalysts are calculated by using first-principle calculation methods. From the view of thermodynamic and dynamic, the mechanism and rate-determining step of electrochemical reduction of CO2 on MN4-G catalysts under the approximate real electrochemical circumstances are illustrated. On this basis, according to the analysis of the relationship between free energy and frontier orbital, the energy, composition and distribution of critical electronic state for electrocatalytic performance of CO2 are revealed. The research approach for the improvement of electrocatalytic activity and selectivity of MNx-G catalysts is proposed based on the influence factors optimization of controllable critical electronic state, which will provide a new theoretical basis for the study of novel single metal atom embedded in graphene catalysts for electrochemical reduction of CO2.

金属单原子催化剂的设计与合成，使得金属催化剂利用率最大化，极大地推动了高性能催化剂研究。类卟啉结构金属单原子内嵌石墨烯(MNx-G)在CO2电化学还原反应中展现了良好的电化学稳定性，但催化活性不足、选择性欠佳限制了它的应用。如何提升MNx-G催化性能是当前CO2电催化研究的重大科学问题。本项目拟采用第一性原理计算方法，以MN4-G催化剂为研究对象，通过CO2电化学还原反应各基元步骤的反应自由能变化和过渡态能垒计算，从热力学和动力学角度，阐明近似真实电化学环境下MN4-G催化剂的CO2电化学还原反应机理，明确反应速率决定步骤。在此基础上，通过解析反应自由能与前线轨道之间的关系，揭示支配CO2电催化性能的关键电子态能量、构成和空间分布。基于可调控关键电子态影响因素优化，提出增强MNx-G电催化活性和选择性的研究方案，为新型金属单原子内嵌石墨烯CO2电化学还原反应催化剂研究提供新的理论依据。

金属单原子催化剂的设计与合成，使得金属催化剂利用率最大化，极大地推动了高性能催化剂研究。类卟啉结构金属单原子内嵌石墨烯(MNx-G)在CO2电化学还原反应中展现了良好的电化学稳定性，但催化活性不足、选择性欠佳限制了它的应用。提升MNx-G催化性能是当前CO2电催化研究的重大科学问题。本项目采用分子动力学模拟和第一性原理计算方法，通过MNx-G（M=Fe、Co和Ni）催化剂表面水分子构型优化，构筑了稳定的MNx-G催化剂/水分子固-液界面体系；通过固-液界面体系中CO2电化学还原反应各基元步骤的反应自由能变化和过渡态能垒计算，从热力学和动力学角度，阐明了近似真实电化学环境下MNx-G催化剂的CO2电化学还原反应机理，明确了CO2电化学还原产生碳氢化物的关键是形成吸附态CO，还发现了吸附态COOH*形成是NiNx-G和CoNx-G催化剂的CO2电化学还原反应速率决定步骤，而FeNx-G催化剂的反应速率决定步骤则是吸附态CO*形成；在此基础上，依据势能面分解模型，结合固-液体系中催化剂电子态密度分布计算，解析了反应自由能各能量分项与前线轨道能量、构成和空间分布之间的关系，明确了支配CO2电催化性能的关键电子态是MNx-G催化剂中过渡金属原子d-band中心位置；基于此，通过28种不同金属中心原子的MN4-G催化剂表面的CO*和COOH*吸附强度及键长变化计算，探明了MN4-G催化剂的CO2电化学还原催化活性和选择性，为新型金属单原子内嵌石墨烯CO2电化学还原反应催化剂研究提供新的理论依据。