基于CO2电化学还原反应的高效Pd基纳米催化剂的结构设计、可控合成与机理研究

Palladium-based (Pd-based) metal nanocatalysts have been considered as a class of promising catalysts towards the application of electrochemical reduction of CO2 and thus receiving enormous research attention. However, there still existed some urgently scientific questions in the development of high-efficiency Pd-based metal nanocatalysts for electrochemical reduction of CO2. Specifically, it is still lack of effective methods to engineer the parameters (including the percentages of surface atoms, crystal facets, lattice strain, and chemical compositions) of Pd-based metal nanocatalysts, which have been demonstrated as key factors to tune the electro-catalytic performance for the electrochemical reduction of CO2. Due to such a limitation, the relationship between a specific parameter and catalytic properties is still unclear. In addition, the information on the intermediate state and detailed mechanism for electrochemical reduction of CO2, on atomic and molecular scale, is still limited. In this proposed research, we plan to develop some synthetic strategies to control the important parameters (including the percentages of surface atoms, crystal facets, lattice strain, and chemical compositions) of Pd-based nanocatalysts by adjusting the thermodynamic and kinetic factors in the synthesis. Based on the controlled parameters of Pd-based nanocatalysts, we attempt to establish the relationship between each parameter of Pd-based nanocatalysts and the catalytic properties of electrochemical reduction of CO2. Also, we will try to figure out the important intermediate state for the electrochemical reduction of CO2 and further reveal the mechanism on atomic and molecular scale. On the basis of the in-depth understanding for the Pd-based nanocatalysts, we will finally design and synthesize the outstanding Pd-based nanocatalysts towards the electrochemical reduction of CO2.

Pd基金属纳米催化剂在CO2电化学还原反应中具有重要的应用潜力，但当前的研究存在以下关键的科学问题：1）金属纳米催化剂的表面原子比例、表面晶面、晶格应力、以及化学组分等特征参数是调控其催化性能的重要因素。但目前依然缺乏精细调控Pd基金属纳米催化剂的特征参数的有效手段；2）缺乏对Pd基金属纳米催化剂的特征参数与其CO2电化学还原反应的催化性能之间的构效关系分析；3）缺乏原子和分子层面的CO2电化学还原反应的关键过程与微观机理研究。在本项目中，我们拟通过分析各种热力学和动力学参数与Pd基金属纳米晶催化剂可控生长之间的关系，发展出可精细调控Pd基金属纳米晶催化剂的特征参数的有效手段，凝练出Pd基金属纳米晶催化剂的特征参数与CO2电化学还原反应的催化性能之间的构效关系，深入研究发生在Pd基金属纳米晶催化剂表面的CO2电化学还原反应的关键过程与微观机理，最终设计出高效Pd基金属纳米催化剂。

CO2电催化还原不仅为间歇性能源提供了一种新的存储方法，而且实现了碳资源的循环，是实现清洁能源体系的关键技术。发展高效的CO2电还原催化剂是其中的核心，本项目围绕催化剂的表界面精准调控与可控制备、构效关系的建立、以及高效催化剂的设计与研制三个方面展开工作，取得以下主要结果：1）通过对金属Pd催化剂的表面应变进行单变量调控，揭示了CO2电催化还原中的应变效应，发现了表面拉伸应力有助于CO2分子的吸附与活化，提高了CO2电还原催化活性；2）通过构筑具有界面化学耦合作用的复合催化剂，阐明了界面化学耦合作用对CO2电还原活性的作用机制，发现了界面化学耦合作用使催化活性位点的电荷得到重排，富电子的位点有利于CO2分子的吸附与活化，提高了CO2电还原的催化活性。我们将CO2电还原催化剂的研究方法进一步拓展到燃料电池阴极氧还原催化剂的研究上，取得了以下研究成果：3)发展了Pt基超细纳米线的可控制备方法，提出了多尺度耦合设计策略，研制了高活性与耐久性的PtRh以及PtNiRh超细纳米线氧还原电催化剂；4）针对Pt基合金纳米催化剂的耐久性问题，提出通过强化合金组分间的化学键合作用来提高其耐久性的策略，证实了PtGa催化剂中的p-d轨道间的强相互作用有利于催化耐久性的提高，发展了PtGa超细纳米线的可控制备方法，成功制备了高活性与耐久性的氧还原电催化剂。本项目的顺利执行将为高效CO2电还原催化剂的设计提供理论依据，为金属纳米催化剂的表界面精准调控提供方法学依据。此外，本项目在燃料电池阴极催化剂当中的研究将不仅直接提供了三种高效催化剂，而且为氧还原电催化剂的设计提供了新思路。