Holey Graphene-Supported Single Metal Atoms as Highly Efficient Electrocatalysts

电力可以为化学反应提供所需的能量，如将水分解为氢和氧。电催化剂是高效率和低成本的电力驱动化学反应经常需要的材料。单原子催化剂(SACs)是由固体碱(载体)上的单个孤立金属原子组成的。负载型电催化剂具有潜在的高反应速度、可调行为、高耐久性和可回收利用。然而，SACS通常是使用高温工艺生产的，这导致结构复杂且难以表征。在这个项目中，加州大学洛杉矶分校的段向峰博士和他的团队正在开发一种通用的方法，以制备具有明确定义和系统可调结构的石墨胺负载的单金属原子。该团队使用先进的X射线分析和电子显微镜成像方法来明确地确定单个金属原子的排列，并将结构与反应性相匹配，以确定最佳催化剂。这项研究的目标是为下一代可用于移动电子、交通运输和可再生能源的高效电催化剂确定设计标准。SACS可以结合均相催化剂(如高度均匀的活性中心、可调节的配位环境和最大的原子利用效率)和传统多相催化剂的优点(如高耐用性、易与产品分离、良好的可回收性以及易于与电极集成用于电催化)。在这个项目中，段向峰博士正在开发一种通用的方法来制备一系列嵌入到二维石墨烯晶格中的单金属原子，这些原子具有明确的原子结构和系统可调的金属中心(例如，Fe、Co、Ni、Cu、Ru、Pd、Pt)，然后评估它们对各种电化学过程的催化性能。该小组使用扩展X射线吸收精细结构(EXAFS)和X射线吸收近边结构(XANES)分析以及高分辨率透射电子显微镜成像方法来明确识别单个金属原子的局部配位配置。通过实验和理论研究进一步将其与电催化活性相关联，建立了结构-性质关系。由高度结晶的石墨烯支撑的一系列单一金属中心的一般合成可以进行明确的结构鉴定和系统的催化研究(无论是在实验上还是理论上)。其目标是建立结构-属性的相关性，从而确定合理设计具有量身定做的活动、选择性和稳定性的SAS的关键步骤。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Electricity can provide the needed energy for chemical reactions such as the splitting of water into hydrogen and oxygen. Electrocatalysts are materials that are often needed for efficient and cost-effective electricity-driven, chemical reactions. Single atom catalysts (SACs) are composed of single, isolated metal atoms held on solid base (support). Supported electrocatalysts have potentially high reaction speeds, and tunable behavior, high durability, and recyclability. However, SACs are usually produced using high temperature processes that lead to complex and difficult to characterize structures. In this project, Dr. Xiangfeng Duan and his team at University of California, Los Angeles are developing a general approach for the preparation of single metal atoms supported on graphine with well-defined and systematically-tunable structures. The team uses advanced X-ray analyses and electron microscopy imaging approaches to unambiguously identify the arrangement of the single metal atoms, and matches the structures with reactivities to determine the best catalysts. The goal of this research is to define design criteria for the next generation of highly efficient electrocatalysts that could be used in mobile electronics, transportation, and renewable energy. SACs can combine the merits of both homogeneous catalysts (e.g., highly uniform active sites, tunable coordination environment and maximized atom utilization efficiency) and traditional heterogeneous catalysts (e.g., high durability, easy separation from the product, excellent recyclability, and easy integration with electrodes for electrocatalysis). In this project, Dr. Xiangfeng Duan is developing a general approach to prepare a series of single metal atoms embedded in two-dimensional graphene lattices with well-defined atomistic structure and systematically tunable metal centers (e.g., Fe, Co, Ni, Cu, Ru, Pd, Pt), then evaluating their catalytic properties towards various electrochemical processes. The team uses extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) analyses as well as high resolution transmission electron microscopy imaging approaches to unambiguously identify the local coordination configuration of the single metal atoms. These are further correlated with electrocatalytic activities through both experimental and theoretical studies to establish the structure-property relationship. The general synthesis of a series of single metal sites supported by highly crystalline graphene can allow unambiguous structural identification and systematic catalytic investigations (both experimentally and theoretically). The goal is to establish structure-property correlation and thus define the critical steps toward the rational design of SACs with tailored activity, selectivity and stability.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.