Holey Graphene-Supported Single Metal Atoms as Highly Efficient Electrocatalysts

电可以为化学反应提供所需的能量，例如将水分解成氢和氧。电催化剂是一种高效、低成本的电驱动化学反应所需要的材料。单原子催化剂（SACs）是由固定在固体基（载体）上的单个、孤立的金属原子组成的。负载型电催化剂具有潜在的高反应速度、可调行为、高耐久性和可回收性。然而，SACs通常采用高温工艺生产，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制备石墨烯支撑的单金属原子的通用方法，该方法具有良好的定义和系统可调的结构。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识别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。这项研究的目标是确定下一代高效电催化剂的设计标准，这些电催化剂可用于移动电子、交通和可再生能源。SACs可以结合均相催化剂（如高度均匀的活性位点、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（如高耐用性、易于与产物分离、优异的可回收性、易于与电极集成进行电催化）的优点。在这个项目中，段祥峰博士正在开发一种通用的方法来制备一系列嵌入二维石墨烯晶格中的单金属原子，这些原子结构定义明确，金属中心可系统调节（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。该团队使用扩展x射线吸收精细结构（EXAFS）和x射线吸收近边缘结构（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构型。通过实验和理论研究，进一步将其与电催化活性联系起来，建立构效关系。由高结晶石墨烯支持的一系列单金属位点的一般合成可以允许明确的结构识别和系统的催化研究（实验和理论）。目标是建立结构-性能相关性，从而定义具有定制活性，选择性和稳定性的SACs的合理设计的关键步骤。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.