共价有机骨架上氢溢流机理的密度泛函理论研究

Covalent Organic Frameworks (COFs) are a series of coordination polymers constructing from organic ligands and boron-oxygen clusters by self-assembling with strong covalent bonds, which preserve the merits of good stability, large surface area, porosity and extremely low density. They are considered as perspective candidates for hydrogen storage. COFs have exhibited promising hydrogen storage capacities at very low temperatures. However, their hydrogen storage capacities are not satisfactory at room temperature. Hydrogen spillover has been demonstrated as an effective approach to enhance the hydrogen storage capacities in porous materials at ambient temperature. However, the hydrogen spillover mechanism on COFs is not well understood. Therefore, the microcosmic mechanism of adsorption by hydrogen spillover on COFs is studied using density functional theory (DFT) in this project.Based on our recent study,the following works will be done. The effects of metal catalysts on the process of hydrogen spillover are studied. The predictions for hydrogen storage capacities in COFs with different structures are also made. A systematic study is carried out on the effect of structural and surface properties on the hydrogen storage capacities, especially at room temperature. The key factors affecting the hydrogen storage in COFs and the approaches for enhancing the hydrogen storage capacites by spillover are also determined. The results can not only enable us to deepen understanding the microcosmic mechanism of the hydrogen storage in COFs by spillover, but also provide theoretical guidance for the direction preparations of improved COFs substrates experimentally.

共价有机骨架材料（COFs）是由有机配体和硼氧团簇通过共价键自组装而成的配位聚合物，具有良好的热稳定性，大的表面积，高的孔隙率和极其低的密度等优点,被认为是最有希望的氢存储材料。COFs在低温下表现出优异的储氢性能，但室温下却不尽人意。氢溢流被证明是提高多孔材料在室温下储氢性能的有效方法，但有关COFs中氢溢流的微观机理还有很多未解决的问题。本项目拟将使用密度泛函理论对COFs中氢溢流吸附的微观机理展开研究，基于我们最近的研究基础，本课题拟进一步开展如下研究：研究不同金属催化剂对氢溢流过程的影响；预测氢溢流作用后具有不同结构COFs的储氢能力；研究COFs的结构和表面性质与其储氢性能的关系，确定影响其储氢性能的关键因素和提高储氢性能的途径等。这些问题的澄清不仅有助于加深理解氢溢流对COFs储氢性能影响的微观机理，而且可以为实验上定向制备性能优异的COFs基底材料提供理论依据。

共价有机骨架材料（COFs）是近年来提出的一类新型的多孔纳米材料，在低温下表现出优异的储氢性能，但室温下却不尽人意。氢溢流被证明是提高多孔材料在室温下储氢性能的有效方法，但有关COFs的储氢性能及氢溢流现象在其中的微观机理还有很多未解决的问题，因此我们对上述问题进行了深入研究。首先，研究了溢流氢原子在具有不同结构和组分的2D COFs中的化学吸附，通过考虑H原子在其上所有可能的吸附位，构建了饱和团簇模型，预测了氢溢流作用后2D COFs的饱和氢存储能力。研究结果表明：（1）溢流过程可以平稳且可逆地进行；（2）所研究的2D COFs的饱和氢存储密度远远大于它们在室温和中等压力下的物理吸附量，接近或达到了美国能源部（DOE）2010年制定的氢存储目标，因此溢流作用可以使COFs的氢存储能力得到明显提高。其次，研究了H2分子在具有不同结构和组分的2D COFs中的物理吸附行为，预测了其在不同温度和压力下的储氢量，并和其他COFs材料进行了对比。分析了COFs的储氢量随化学组分、表面积、孔直径和等量吸附热等因素的变化关系。研究结果表明：吸附量与化学组分无关，主要取决于表面积，在表面积相差不大的情况下，则取决于孔体积和等量吸附热。最后，对COFs储氢性能的提高提出了一些建设性意见。以上这些结论可以为实验上定向制备性能优异的 COFs 基底材料提供理论依据。