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。它用于农业化肥、能源和制药工业。目前生产氨的方法是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，佐治亚理工学院的穆斯塔法·赛义德教授和他的学生正在探索一种光电化学方法，可以在常压和室温下从氮气和水中生产氨。他们的方法利用了比一粒盐小一万倍的混合纳米颗粒。每个粒子由一个等离子体纳米粒子组成，周围环绕着半导体外壳和催化金属。暴露在光中会激发纳米颗粒中的电子。然后，这些电子被转移到半导体和催化剂上，在那里发生化学转化为氨。该团队的发现可能会扩展到氨合成之外，并影响更广泛的纳米催化领域，纳米催化广泛应用于化工生产、可持续能源和材料化学。该项目正在培训下一代科学家，并吸引亚特兰大大都市区历史悠久的黑人学院和大学(HBCU)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，以及将固体Au等离子体纳米粒子放置在中空纳米催化剂中的Au纳米笼子。然后使用这些纳米催化剂在(光)电化学系统中研究了在常温条件下将氮(N_2)转化为氨(NH_3)的反应，测量了反应速度和催化效率。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气还原反应的全反应机理。以过渡催化金属(如Ru、Pd)作为掺杂剂、助催化剂和等离子体激活剂与半导体和等离子体金属(Au)结合，利用超快泵浦探测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出具有较长复合时间的活性光电催化剂，从而有利于氮气的光电还原反应。该团队在纳米颗粒合成、实验室规模光电化学测试和最先进的光谱学方面拥有丰富的经验，并辅之以理论研究，以获得对实现氮基肥料生产的光电化学固氮过程的基本了解。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。

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.