CAREER: Single-Atom Alloy Nanocrystals for Catalyzing Sustainable Nitrogen Cycling

化肥的工业生产--由能源密集型、依赖化石燃料的Haber-Bosch(H-B)工艺产生的氨(NH3)--扰乱了自然氮循环，导致地下水受到硝酸盐(NO3-)的污染。该项目利用电化学将硝酸盐化合物与氢气(可持续地从水中提取)反应生成NH3，同时分解硝酸盐污染物并恢复氮循环的平衡。具体地说，这项研究的重点是发现和设计能够实现由可再生电力驱动的高效硝酸盐转化为氨的催化剂。除了技术方面，该项目将在催化、化学和工程的界面上培训来自不同群体的学生。这项研究将与教育和外联工作相结合，以说明日常生活中可持续性的重要性，同时激发K-12青年，特别是来自低收入家庭的青年对STEM的兴奋。电化学硝酸盐还原反应(NO3RR)提供了一条潜在的有吸引力的分布式氨生产路线，因为它利用硝酸盐污染物作为氮源，从而绕过了与H-B过程相关的强N≡N三键的激活。该项目将开发用于NO3RR的单原子合金(SAA)电催化剂的设计策略，并促进对催化活性中心和基本机理的基本理解。该项目建立在一个中心假设的基础上，即在铜纳米晶体表面掺杂孤立的金属原子(例如，铂、钯、Rh或Ru)会产生明确的位置，激活水分子并产生溢出到铜的氢原子。氢原子在低过电势下氢化N物种，并通过窄分布的单原子d态选择性地调整NO3RR表面中间体的结合强度，从而高速生产NH3，可能会超越吸附能量标度限制。先进的表征技术将促进催化剂的合成、表征和电化学评价，这些技术包括表面增强红外吸收光谱、差示电化学质谱、原位X射线吸收光谱、先进的电子显微镜以及密度泛函理论等计算工具。该项目的教育部分包括(1)将研究纳入课程，(2)跨学科学生培训，(3)让科学和工程领域的不同代表性不足的学生参与，以及(4)通过弗吉尼亚理工大学加强工程多样性中心和神奇宇宙：儿童博物馆的暑期计划实施以STEM为基础的外展计划。此外，新成立的弗吉尼亚清洁能源和催化俱乐部将作为促进学生培训的平台。外展计划还包括开发一个基于互动游戏的教学平台--“我的世界中的可持续城市”，它将为年轻学生提供设计和建设未来可持续城市的机会。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。

The industrial production of fertilizer – produced from ammonia (NH3) generated by the energy-intensive, fossil fuel-dependent Haber-Bosch (H-B) process - has disrupted the natural nitrogen cycle, resulting in groundwater pollution from nitrates (NO3-). The project utilizes electrochemistry to react nitrate compounds with hydrogen (derived sustainably from water) to manufacture NH3, while simultaneously decomposing the nitrate pollutants and restoring balance to the nitrogen cycle. Specifically, the research focuses on the discovery and design of catalysts that enable efficient nitrate-to-ammonia transformation driven by renewable electricity. Beyond the technical aspects, the project will train students from diverse groups at the interface of catalysis, chemistry, and engineering. The research will be integrated with educational and outreach efforts to illustrate the importance of sustainability in daily life while stimulating excitement for STEM amongst K-12 youth, especially those from low-income families. The electrochemical nitrate reduction reaction (NO3RR) offers a potentially attractive distributed NH3 production route, because it utilizes nitrate pollutants as the N-source, thus circumventing activation of the strong N≡N triple bond associated with the H-B process. The project will develop design strategies for single-atom alloy (SAA) electrocatalysts for the NO3RR and advance the fundamental understanding of both the catalytic active sites and the elementary mechanisms. The project is built on the central hypothesis that surface doping of Cu nanocrystals with isolated metal atoms (for example, Pt, Pd, Rh, or Ru) creates well-defined sites that activate water molecules and generate H-atoms that spill over to the Cu. The H-atoms hydrogenate N-species at low overpotentials and selectively tailoring of the binding strength of NO3RR surface intermediates through narrowly distributed d-states of single atoms for high-rate production of NH3, can potentially go beyond adsorption-energy scaling limitations. Catalyst synthesis, characterization, and electrochemical evaluation will be facilitated by advanced characterization techniques including operando surface-enhanced infrared absorption spectroscopy, differential electrochemical mass spectrometry, in-situ X-ray absorption spectroscopy, advanced electron microscopy, and computational tools such as density functional theory. The educational components of the project include (1) integrating research into the curriculum, (2) interdisciplinary student training, (3) involving diverse underrepresented students in science and engineering, and (4) implementing STEM-based outreach programs through the Center for Enhancement of Engineering Diversity at Virginia Tech and summer programs at Wonder Universe: A Children’s Museum. In addition, the newly launched Virginia Clean Energy and Catalysis Club will be leveraged as a platform to promote student training. The outreach plan also includes the development of an interactive play-based pedagogical platform, “Sustainable City in Minecraft,” that will provide young students the opportunity to design and construct a futuristic sustainable city.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.