基于二维共轭高分子纳米结构的光催化二氧化碳还原体系可控构筑及其反应机理研究

The severe environmental issues caused by the emission of CO2 and increasing energy crisis have triggered broad interests in developing sustainable techniques to convert CO2 into value added chemicals and chemical fuels using solar energy. Thus, design and synthesis of highly efficient photocatalysts and elucidation of the basic chemical and physical principles during photocatalytic CO2 reduction by mimicking natural photosynthesis is highly desirable. Two-dimensional conjugated polymer semiconductors are a unique class of photocatalytic system which could exhibit high photoabsorption, high surface area with tunable optical and electronic structures. Therefore, they are very promising for applications in photocatalytic CO2 reduction and attracting increased attention recently. Due to the highly tunable structures of conjugated polymer systems, the catalytic activity could be rationalized via introducing catalytic active centers with optimized structures. However, current photocatalytic systems based on conjugated polymers are very limited. Meanwhile, the structure-property relationships on polymer-based semiconductors are still poorly understood. Especially, when highly active metal centers are incorporated into the catalytic systems, the photocatalytic CO2 reduction process and mechanism are still not clear. More importantly, the photocatalytic efficiency and product selectivity are still the bottleneck in this research field. In this proposed study, we first select and screen some different two-dimensional polymer structure with different metal centers to identify the most active and effective photocatalysts. Subsequently, we will utilize the advanced characterization techniques such as SRPES / XPS / UPS / NAXAFS along with the in situ reaction device coupled with in-line mass spectrometry to systematically study the surface structure of the catalyst, transition species adsorbed on surface, and other related information. The purpose of this proposed study is to elucidate the mechanisms that are responsible for photocatalytic CO2 reduction on metal centers and to reveal the key factors affecting the catalytic activity both at the atomic and molecular level. This study will not only point out the factors affecting the catalytic properties but also can provide experimental and theoretical guides for the design and synthesis of highly active photocatalysts in the future.

日益加重的二氧化碳排放导致的环境问题与日益严峻的能源危机使得通过模仿自然界光合作用的基本原理，发展与设计高效光催化剂体系，利用太阳能将CO2催化转化为碳基燃料与化学原料的技术具有重要的意义。结构可控的共轭有机二维高分子半导体在CO2催化转化中具有潜在的应用前景，通过引入金属催化中心，可以得到具有最优化电子结构、能带位置与催化活性位点的催化体系。针对目前高分子催化体系研究有限，反应原理与规律没有得到深入理解，CO2光还原反应中的催化活性低与产物选择性差等难点，本项目拟从设计与合成具有可控能带结构的二维高分子半导体材料出发，构筑非贵金属金属催化活性中心，利用同步辐射等先进表征手段探索金属中心与半导体间电荷动力学行为并揭示CO2还原反应机理。期望通过深入研究，系统揭示还原反应的作用机制与物理化学过程，阐明结构与性能的构效关系，为未来研究此类材料在光催化中的应用奠定基础，促进该领域进一步发展。

本项目围绕二维共轭高分子光催化材料的设计、合成、及光催化水分解及二氧化碳还原反应过程的基本物理化学问题和反应机理开展研究。我们通过发展新的二维共轭高分子结构设计与合成方法学，调控材料的化学与电子结构，实现了对高分子催化活性中心的精准构筑，并进一步对二维共轭高分子的催化性能与催化路径进行优化和调控，筛选得到了一批具有不同化学结构且具有优异光催化性能的高分子材料并制备出高效稳定的光电化学器件，成功实现高效、高选择性光催化水分解及二氧化碳还原。所设计出的高分子光催化材料实现了光化学合成过氧化氢0.78%的太阳能到化学能能量转化效率值且在光催化还原二氧化碳高效制备甲烷应用中产物选择性达到87%。我们利用同步辐射光谱技术、超快吸收光谱技术、原位谱学技术等先进表征手段并结合第一性原理计算，从原子和分子水平深入揭示出二维共轭高分子材料催化中心局域环境、光生电荷分离效率与反应机理，阐明了影响光催化活性的关键实验参数与电荷动力学调控机制，初步建立了高分子材料结构与性能之间的构效关系。本项目发展了新的二维共轭高分子制备方法，在二维共轭高分子结构与催化反应机理及电荷动力学调控等方面进行了系统深入研究，充分展示了二维共轭高分子结构可设计的优越性，证实二维共轭高分子在人工光合成研究领域有极大的应用前景，为今后开展相关研究奠定了基础。