Collaborative Research: CAS-SC: Electrochemical Approaches to Sustainable Dinitrogen Fixation

在化学系化学催化项目的支持下，罗格斯大学的Alan Goldman教授、耶鲁大学的Patrick Holland教授和北卡罗来纳大学教堂山分校的Alexander Miller教授正在研究利用分子催化剂将大气中的氮气（N2）电化学转化为氨（NH3）的原理。这项研究将为寻找可持续替代品以取代目前以化石燃料为基础的氨的途径奠定基础。仅使用可再生能源生产NH3的低温电化学固氮工艺可以通过消除对天然气的依赖和分散肥料生产来改变全球农业，从而大幅减少二氧化碳排放。除了肥料，电化学固氮还可以实现无碳氨的生产，用于储存和运输可再生能源，直接用作电力设施或运输的燃料，或转化为氢。罗格斯大学（Rutgers University）农业经济学家和可持续发展专家盖尔·霍克曼（Gal Hochman）教授的合作有助于将基础化学和催化研究与可能的未来应用联系起来。这三个研究小组已经建立了一个理想的合作环境，以培养未来的科学领导者。除了研究之外，学生们和pi们还在进一步发展“固氮者”（NitrogenFixers.org）的外展项目，其中包括面对面、虚拟远程和自己动手做的电化学和可持续能源实验。它通过展示化学研究的重要性和兴奋性来激励初高中学生，包括N2固定和可持续性的重要性。在这个合作项目中，罗格斯大学的艾伦·戈德曼教授、耶鲁大学的帕特里克·霍兰德教授和北卡罗来纳大学教堂山分校的亚历山大·米勒教授组成的研究小组正在研究化学领域的一项重大挑战，即利用分子催化剂为哈伯-博世过程提供电化学替代方案，将大气中的氮（N2）转化为氨（NH3）。该研究方法背后的指导机制假设是，双金属分裂形成金属氮化物配合物可以提供高活性、高选择性的NH3（超过H2）和低过电位的电化学氮还原。该合作团队寻求详细的电化学N2结合和分裂机制的理解，以及随后的质子耦合电子转移（PCET）到氮化物，这可以用来发现新的氨合成催化剂。其中一个重点是使用平行实验工作流程来改进反应条件。机理研究将集中在实现催化的两个关键步骤（N2解理和氮化物络合物还原）。电化学诱导的N2结合和氮化物络合物的形成机制是利用计算研究和实验电化学研究相结合的方法来解决的。下一步氮化物的还原也与N2的其他还原机制有关，因此具有广泛的相关性。N2还原的分子电催化仍然远远落后于其他反应，如CO2还原和H2演化，但在这个项目中，平行电解方法和分子水平机制细节的结合有望导致有效的电催化系统，这些系统定义明确，并适合继续开发。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。

With the support of the Chemical Catalysis program in the Division of Chemistry, Professors Alan Goldman of Rutgers University, Patrick Holland of Yale University, and Alexander Miller of the University of North Carolina at Chapel Hill are studying the principles of electrochemical conversion of atmospheric nitrogen (N2) to ammonia (NH3) using molecular catalysts. The research will establish a foundation for efforts to discover sustainable alternatives to replace current fossil fuel-based routes to ammonia. A low-temperature electrochemical N2 fixation process for NH3 production using only renewable energy could transform global agriculture by eliminating dependence on natural gas and decentralizing fertilizer production, thus substantially mitigating CO2 emissions. Beyond fertilizer, electrochemical N2 fixation could also enable carbon-free production of ammonia for the storage and transportation of renewably produced energy, for direct use as fuel for electric utilities or transportation or for conversion to hydrogen. Connecting the fundamental chemistry and catalysis research with possible future application is aided by collaboration with Professor Gal Hochman of Rutgers University, an agroeconomist and sustainability expert. The three research groups have established a collaborative environment ideal for training future leaders in science. In addition to research, the students and PIs are further developing the NitrogenFixers.org outreach program, which includes live in-person, virtual remote, and do-it-yourself experiments on electrochemistry and sustainable energy. It inspires middle and high school students by demonstrating the importance and excitement of chemical research, including the importance of N2 fixation and sustainability. In this collaborative project, the research groups of Professors Alan Goldman of Rutgers University, Patrick Holland of Yale University, and Alexander Miller of the University of North Carolina at Chapel Hill are working on a grand challenge in chemistry that relates to providing electrochemical alternatives to the Haber-Bosch procedure for conversion of atmospheric nitrogen (N2) to ammonia (NH3) using molecular catalysts. The guiding mechanistic hypothesis behind the research approach is that bimetallic splitting of dinitrogen to form metal nitride complexes can give high activity, high selectivity for NH3 (over H2), and low overpotential for electrochemical nitrogen reduction. The collaborative team seeks detailed mechanistic understanding of electrochemical N2 binding and splitting, and subsequent proton-coupled electron transfer (PCET) to nitride, which can be leveraged to discover new catalysts for ammonia synthesis. One highlight is the use of a parallel experimentation workflow for refinement of reaction conditions. Mechanistic studies will focus on the two key steps enabling catalysis (N2 cleavage and nitride complex reduction). Electrochemically induced N2 binding and the mechanism of formation of nitride complexes are being addressed using computational studies integrated with experimental electrochemical studies. The reduction of the nitrides in the following step is relevant to other mechanisms of N2 reduction as well, and therefore has broad relevance. Molecular electrocatalysis of N2 reduction remains far behind other reactions such as CO2 reduction and H2 evolution, but the combination of parallel electrolysis methodology and molecular-level mechanistic detail in this project promises to lead to effective electrocatalytic systems that are well-defined and amenable to continued development.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.