Investigation of (Photo) Electrocatalytic Conversion of N2 to NH3 under Ambient Conditions Using Hybrid Hollow Plasmonic Nanostructures

氨是世界上广泛生产的化学品之一。它被用于农业肥料、能源和制药工业。目前生产氨的方法需要将反应物加热到非常高的温度和高压，这需要大量的能量。在化学系大分子、超分子和纳米化学项目的支持下，乔治亚理工学院的Mostafa El-Sayed教授和他的学生正在探索一种光电化学方法，该方法可以在常压和室温下从氮和水中产生氨。他们的方法是利用比一粒盐小1万倍的混合纳米粒子。每个粒子由一个等离子体纳米粒子组成，被半导体壳层和催化金属包围。暴露在光下会激发纳米粒子中的电子。然后这些电子被转移到半导体和催化剂上，在那里化学转化为氨。该团队的发现可能会延伸到氨合成之外，并影响更广泛的纳米催化领域，纳米催化广泛应用于化学生产、可持续能源和材料化学。该项目正在培养下一代科学家，并吸引亚特兰大大都会地区传统黑人学院和大学（HBCUs）的学生。El-Sayed教授和他的团队还通过实验室参观和在STEM招聘会和当地学校的公开演讲来展示他们的研究。合成了各种金属（如Au、Pd和Ru）纳米笼，杂化双壳（如Ag-Au、Au-Pd、Au-Ru）纳米笼，以及在空心纳米催化剂内放置固体Au等离子体纳米颗粒的Au纳米笼。然后在（光）电化学系统中使用这些纳米催化剂探索了在环境条件下氮（N2）转化为氨（NH3）的过程，并测量了反应速率和催化效率。利用原位表面增强拉曼光谱和原子力显微镜研究了电化学氮还原反应的完整反应机理。利用过渡催化金属（如Ru、Pd）作为掺杂剂、助催化剂和等离子体增强剂与半导体和等离子体金属（Au），利用超快泵浦探针光谱研究了它们对载流子复合和电子注入动力学的影响。这些实验有助于设计具有较长复合时间的活性光电催化剂，从而促进光电氮还原反应。该团队在纳米颗粒合成、实验规模的光电化学测试和最先进的光谱学方面拥有丰富的经验，并辅以理论研究，以获得对光电化学固氮过程的基本理解，从而实现氮基肥料的生产。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。

Ammonia is one of the widely produced chemicals in the world. It is used in agricultural fertilizer, energy, and in the pharmaceutical industry. The current method for producing ammonia involves heating the reactants to very high temperatures and at high pressures, which requires large amounts of energy. With support from the Macromolecular, Supramolecular, and Nanochemistry Program in the Division of Chemistry, Professor Mostafa El-Sayed at the Georgia Institute of Technology and his students are exploring a photo-electrochemical approach that would produce ammonia from nitrogen and water at atmospheric pressure and room temperature. Their approach makes use of hybrid nanoparticles that are 10,000 times smaller than a grain of salt. Each particle consists of a plasmonic nanoparticle, surrounded by a semiconductor shell and catalytic metal. Exposure to light excites the electrons in the nanoparticle. These electrons are then transferred to the semiconductor and the catalyst, where the chemical conversion to ammonia occurs. The team's discoveries could extend beyond ammonia synthesis and impact the broader field of nanocatalysis, which is widely used in chemical production, sustainable energy, and materials chemistry. The project is training the next generation of scientists and is engaging students at historically black colleges and universities (HBCUs) in the Atlanta metropolitan area. Professor El-Sayed and his group also showcase their research through lab tours and public presentations at STEM career fairs and local schools. Various metal (e.g., Au, Pd, and Ru) nanocages, hybrid double shell (e.g., Ag-Au, Au-Pd, Au-Ru) nanocages, and Au nanorattles where a solid Au plasmonic nanoparticle is placed inside the hollow nanocatalyst are synthesized. The conversion of nitrogen (N2) to ammonia (NH3) under ambient conditions is then explored using these nanocatalysts in a (photo) electrochemical system, which measures the reaction rate and catalytic efficiency. In-situ surface-enhanced Raman spectroscopy and atomic force microscopy are performed to study the full reaction mechanism during electrochemical nitrogen reduction reaction. Transition catalytic metals (e.g., Ru, Pd) are utilized as dopants, co-catalysts, and plasmon enhancers with semiconductor and plasmonic metals (Au) to study their effects on the charge carrier recombination and the dynamics of electron injection using ultrafast pump-probe spectroscopy. These experiments help to design an active photo-electrocatalyst with longer recombination time, therefore facilitating the photo-electrochemical nitrogen reduction reaction. The group's extensive experience in nanoparticle synthesis, bench scale photo-electrochemical testing and state of the art spectroscopy is complemented by theoretical studies to gain a fundamental understanding of photo-electrochemical nitrogen fixation processes that enable nitrogen-based fertilizer production.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.