CAREER:Engineering Interphases for Li-Mediated Nitrogen Reduction at Ambient Conditions

化学制造业是国家经济的主要贡献者，生产从化肥和药品到塑料和燃料的所有产品。尽管化学工业成功地生产了对日常生活至关重要的化学品和材料，但仍存在与碳足迹和化学制造集中化相关的问题。许多化学工艺都是在大规模的集中工厂中进行的，因为较小的生产能力在经济上是不可行的。一个例子是哈伯-博世工艺，该工艺生产含氮肥料所需的大部分氨。该过程在高温和高压下以集中方式大规模运行。此外，哈伯-博世工艺占全球二氧化碳排放量的1 - 2%。氨的电化学合成能够以较低的碳足迹和较小的生产能力进行有竞争力的制造。通过施加电势来驱动反应，而不是使用温度和压力，化学过程可以在更温和的条件下，以更小的规模，更接近最终用户，例如以分布式方式运行。该CAREER项目将专注于基础研究，研究如何使用锂基电化学系统提高氨生产电化学过程的选择性和生产率。该项目开发的方法将推进如何在高反应性电极-电解质界面选择性地合成一种化学品（氨）。研究知识将适用于一个外展计划，重点是教学质量和能量平衡的重要性，以中学生使用。了解日常化学品和材料的来源以及它们的生产方式将有助于对其对社会和环境的影响进行批判性评估。迄今为止，由于竞争性析氢反应，使用电化学氮还原的合成方法在水性电解质中具有差的选择性和低的反应速率。为了提高氮还原的选择性，该项目将研究在非水电解质中的氨合成，因为质子活性可以很好地控制，具有锂金属介导的化学，这允许在环境条件下进行氮固定。将用原位和非原位光谱方法研究电解质组合物对锂覆盖电极上存在的固体电解质界面（SEI）物质的影响。假设SEI结构和组成控制氮还原相对于竞争性氢释放的选择性。该项目将解决运输限制的性质及其对耦合运输动力学的影响。作为这项工作的结果，将获得在非水溶剂中有效的电化学氨生产的必要的界面步骤的基本理解。这种理解将转化为在SEI中发生的非水电解质中的其他电合成反应。该项目分为三个目标。目标1解决了工程化固体电解质界面以促进期望的界面反应。目的二是研究设计适用于非水溶剂的全憎性电极，以实现氮快速迁移到活性中心。最后，目标3将侧重于阳极和电解质设计的质量和能量平衡。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。

Chemical manufacturing is a key contributor to the Nation's economy, producing everything from fertilizers and pharmaceuticals to plastics and fuels. Despite the successes of the chemical industry to produce chemicals and materials critical to everyday living, there are issues associated with the carbon-footprint and centralization of chemical manufacturing. Many chemical processes are run in centralized plants at large scale because smaller capacities are not economically viable. An example is the Haber-Bosch process that produces a large portion of the ammonia needed for nitrogen-containing fertilizers. The process is run at high temperatures and pressures and at large scale in a centralized fashion. Furthermore, the Haber-Bosch process contributes to 1 - 2% of global carbon dioxide emissions. Electrochemical synthesis of ammonia could enable competitive manufacture at a lower carbon footprint and with a smaller production capacity. By applying an electrical potential to drive reactions instead of using temperature and pressure, chemical processes can be run at milder conditions, at smaller scales, and closer to the end user, e.g. in a distributed fashion. This CAREER project will focus on fundamental research to study ways to improve selectivity and production rates of an electrochemical process for ammonia production using a lithium based electrochemical system. Methods developed in the project will advance how to selectively synthesize one chemical (ammonia) over another at the highly reactive electrode-electrolyte interface. The research knowledge will be adapted to be used in an outreach program focused on teaching the importance of mass and energy balances to middle school students. Understanding where everyday chemicals and materials come from and how they are produced will allow for critical evaluation of their impact on society and the environment. To date, synthesis methods using electrochemical nitrogen reduction suffer from poor selectivity and low reaction rates in aqueous electrolytes due to the competing hydrogen evolution reaction. In order to improve selectivity for nitrogen reduction, this project will investigate ammonia synthesis in nonaqueous electrolytes, as the proton activity can be well-controlled, with a lithium metal-mediated chemistry, which allows for nitrogen fixation at ambient conditions. The effect of the electrolyte composition on the solid-electrolyte interphase (SEI) species present on the lithium-covered electrode will be studied with both in situ and ex situ spectroscopic methods. The SEI structure and composition is hypothesized to control the selectivity for nitrogen reduction versus competing hydrogen evolution. The project will address the nature of the transport limitations and its impact on the coupled transport-kinetics. As a result of this work, fundamental understanding of the necessary interfacial steps for efficient electrochemical ammonia production in a nonaqueous solvent will be obtained. This understanding will translate to other electrosynthetic reactions in nonaqueous electrolytes that take place at SEIs. The project is structured into three aims. Aim 1 addresses engineering the solid electrolyte interphase to promote desired interfacial reactions. Aim 2 will study the design of omniphobic electrodes for non-aqueous solvents to achieve fast nitrogen transport to the active sites. Finally, Aim 3 will focus on the mass and energy balances for anode and electrolyte design.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.