CAREER: Engineering the Reactivity of Single Atom Electrocatalysts Beyond their Active Site

利用风能和太阳能等可再生能源发电变得越来越便宜和容易获得。 然而，为了实现我们国家的脱碳目标，需要能够利用这种可再生电力来生产二氧化碳（CO2）排放量低的有用化学品和燃料的技术。电化学工艺正准备解决这一关键需求。例如，水的电化学裂解可以产生绿色氢，而绿色氢的氧化可以根据需要产生碳自由能。 但是这些过程的可行性取决于电化学反应所需的催化材料的性能和成本。这些催化剂通常由稀有和昂贵的金属如铂、钯和铱组成。改善这些材料性能的一种策略是将金属作为单个原子分散在高表面积载体上。 这些“单原子”催化剂（SAC）提供最大的金属使用效率并显示出独特的催化性能。 但关键的基本问题仍然是这些催化剂如何进行电催化反应，以及在操作条件下它们的真实结构是什么。 该项目旨在发展对SAC电化学催化的基本理解，并利用这种理解来设计具有改进性能和贵金属使用效率的新材料。这项研究将与教育工作相结合，旨在吸引来自代表性不足的群体的学生，特别是拉丁裔学生，并让他们对催化剂在可持续发展中的作用感到兴奋。目前，单原子电催化剂的活性位点结构缺乏均匀性。 为了解决这一问题，该项目将利用原子层沉积（ALD）来合成催化剂，这些催化剂具有沉积在精确合成的金属氧化物纳米晶载体上的高度均匀的催化活性位点。 结合特定位点和原位光谱将用于了解活性位点的原子结构以及它们的结构在反应条件下如何演变。在确定了这些活性位点的性质之后，将在它们的结构和催化行为之间建立联系。这些结构-性质关系将被用来设计具有最佳活性的催化剂，系统地调整金属位点与氧化物载体的键合。这种连续调谐将通过电化学离子插入金属氧化物载体来实现。除了了解催化位点如何响应与其支持物结合的变化外，该项目还将进一步展示如何通过改变其运行的电化学介质来控制其特性。在这些研究中开发的见解将用于设计催化剂，用于使用甘油（生物柴油的主要副产品）作为代表性底物的选择性电化学氧化反应。该奖项反映了NSF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 generation from renewable sources, such as wind and sunlight, is becoming increasingly cheap and available. To meet our nation’s decarbonization goals, however, technologies are needed that can leverage this renewable electricity to produce useful chemicals and fuels with low carbon dioxide (CO2) emissions. Electrochemical processes are poised to address this critical need. For example, the electrochemical splitting of water can produce green hydrogen, while the oxidation of green hydrogen can yield carbon free energy on demand. But the viability of these processes depends on the performance and cost of catalytic materials needed for the electrochemical reactions. These catalysts are typically composed of rare and expensive metals such as platinum, palladium, and iridium. One strategy to improve the performance of these materials is to disperse the metal as individual atoms on a high surface area support. These “single-atom” catalysts (SACs) provide maximum metal usage efficiency and display unique catalytic properties. But key fundamental questions remain about how these catalysts carry out electrocatalytic reactions and what their true structure is under operating conditions. The project seeks to develop a fundamental understanding of electrochemical catalysis over SACs, and use this understanding to design new materials with improved performance and precious metal usage efficiency. The research will be integrated with educational efforts aimed at engaging students from underrepresented groups, particularly LatinX students, and exciting them about the role of catalysis in sustainability. Currently, single-atom electrocatalysts suffer from a lack of uniformity in their active site structures. To address that issue, the project will utilize atomic layer deposition (ALD) to synthesize catalysts with highly uniform catalytic active sites deposited on precisely synthesized metal oxide nanocrystalline supports. A combination of site-specific and in situ spectroscopies will be used to understand the atomic structure of the active sites and how their structure may evolve under reaction conditions. Having identified the nature of these active sites, links will be made between their structure and catalytic behavior. These structure-property relationships will be leveraged to design catalysts with optimal activity, systematically tuning the bonding of the metal site to the oxide support. This continuous tuning will be enabled by electrochemical ion insertion into the metal oxide support. In addition to understanding how the catalytic sites respond to changes in bonding to their support, the project will further demonstrate how their properties can be controlled by changing the electrochemical medium in which they operate. The insights developed in these studies will be used to design catalysts for selective electrochemical oxidation reactions using glycerol, a major byproduct of biodiesel, as a representative substrate.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.