卟啉基共价三嗪框架固载的单原子金属电还原二氧化碳研究

The electrocatalytic reduction of carbon dioxide to value-added chemicals can not only alleviate the greenhouse effect, but also is an effective way to transform waste into treasure. However, most of the electrocatalysts have low Faraday efficiency and stability. Single metal atom catalysts (SACs) often exhibit excellent catalytic performance with maximized atom efficiency. However, the fabrication of SACs remains great challenge due to their easy aggregation. The key point is to develop suitable supports that possess strong interaction with the single metal atoms. Porous covalent triazine framework materials (CTFs) have high CO2 adsorption uptakes and super chemical stability. In order to solve the low efficiency and stability of the most electrocatalysts for CO2, this project will fabricate single metal atoms anchored on porous porphyrinic triazine-based frameworks via a simple ionothermal method, resulting in highly reactive and stable SACs for electrocatalytic reduction of CO2. Herein, the porphyrin struts in porous porphyrinic triazine-based frameworks involving four pyrrolic nitrogen sites in a square-planar geometry are very promising and offer inherent conditions to firmly trap single metal atoms. Through this project, a series of stable single metal atoms anchored on porphyrins-based covalently triazine framework materials for highly efficient and electrocatalytic reduction of carbon dioxide will be obtained. A general method for preparation of SACs will be summarized. The mechanism of metaloporphyrins-based CTFs materials for electrocatalysis of CO2 will be proposed coupled with experiments and theoretical calculation. The relationship between the structure and property of the electrocatalysis will be establised. The project has a great significance for reducing carbon dioxide emissions and eliminating the greenhouse effect.

将二氧化碳电催化还原为附加值高的化学品，不仅能缓解温室效应，而且也是变废为宝的一条途径。但目前大多数电催化剂的法拉第效率和稳定性亟待提高。单原子金属催化剂(SACs)具有最大的原子效率，在很多反应中表现出很高的活性。但因单原子易于团聚，因此获得稳定的SACs仍然面临着巨大的挑战，而选择合适的载体来固载单原子金属是关键。多孔共价三嗪框架材料（CTFs）具有强的CO2富集能力和超强的化学稳定性等优点。本项目以多孔卟啉基CTFs上的吡咯氮位点来稳定单原子金属，采用离子热法制备稳定的、固载在多孔卟啉基CTFs上的金属单原子，使其能高效、持久性的电还原CO2。通过本项目的实施，获得系列高效、稳定的电还原CO2的单原子金属催化剂，总结制备该材料的通用方法，结合理论计算阐明单原子金属催化剂进行电还原CO2的机制，建立结构与性能的关系。本项目对二氧化碳减排、消除温室效应具有重要意义。

随着工业化进程加快，温室气体二氧化碳的排放量剧增导致环境恶化，亟需将空气中二氧化碳浓度控制在合理范围。利用清洁可持续电能将其电催化转化为附加值高的化学品， 是缓解温室效应同时也是变废为宝的一条重要途径，但大多数电催化剂的法拉第效率、活性和稳定性亟待提高。考虑到多孔共价三嗪框架材料（CTFs）具有强的CO2富集能力、超强的化学稳定性等优点，本项目采用离子热法设计合成了多孔卟啉基CTFs上的吡咯氮位点来稳定不同的单原子金属如Ni等，制备了稳定的、固载在多孔卟啉基CTFs上的金属单原子催化剂，发现Ni单原子可以在较宽的电势窗口中以接近100%选择性电催化CO2产CO，并且催化剂能够长时间工作而效率没有明显降低。同时，针对电催化CO2制乙烯仍面临活性低、选择性差等难题，其很大程度上受限于单一活性位点的多电子转移过程和缓慢的C-C耦合步骤，提出了串联催化思路，利用非贵金属单原子Ni产CO，而Cu纳米催化剂可以进行CO-CO耦合的优势，进行串联催化来提升CO2制乙烯的选择性。通过在卟啉基三嗪框架锚定Ni单原子和负载Cu纳米颗粒，制备了非贵金属基的串联电催化剂。催化时单原子Ni高效将CO2还原为中间体CO，生成的CO马上被临近的Cu纳米催化剂进行C-C耦合反应高效转化为乙烯。因此，与非串联催化剂主要产甲烷相比，乙烯的法拉第效率提高了5倍(-1.1V vs. RHE)，由9.6% 提高到57.3%，优于目前已经报导其他电催化剂。此外，PTF(Ni)/Cu表现出良好的稳定性，连续电解11 h后仍能保持约91%的初始活性。通过本项目的实施，获得了系列高效、稳定的电还原CO2的单原子金属催化剂，发现了两种制备该材料的通用方法，通过原位红外拉曼紫外结合理论计算阐明了单原子金属催化剂进行电还原CO2的机制，初步建立了不同单原子催化剂结构与电催化性能的关系，为后续进一步设计制备高效稳定的电催化二氧化碳催化剂提供了重要参考。