Synergy between oxide and nitride phases of a novel composite cathode for high-temperature electrocatalytic NH3 synthesis

该项目的重点是一种在常压下从氮气和水中电催化制氨的策略。氨(NH3)生产的传统路线是哈伯-博世(HB)工艺，该工艺包括在高温和高压下通过热催化反应转化氮气和氢气。由于氨在农业(大约80%的氨生产用于制造化肥)、交通、制药、炸药以及能源部门作为一种有前途的间接储氢介质的广泛使用，对氨的需求一直在不断增加。考虑到对NH3日益增长的需求，以及二氧化碳排放量大的传统工艺的高能源密集性，更清洁、能源密集度较低的替代方案将对经济和环境产生重大影响。此外，该项目有可能为材料的合成和表征、机理步骤和电催化现象提供新的见解，可以转化为其他催化和电催化系统，用于环境重要的过程，如电催化还原NOx和二氧化碳电解。这里提出的研究活动将与俄亥俄州立大学现有的教育和推广计划相结合，最终目标是增加学生在STEM领域的参与率、保留率和毕业率。该项目的总体目标是开发用于固体氧化物电解槽(SOEC)型反应器中氨的高温电合成的高活性和选择性阴极电催化剂。高温(400-600摄氏度)电催化氨合成将包括H2O的解离形成H+和O2-，以及N2的电催化活化，然后与H+反应生成NH3。在该方案中，O2-离子通过氧化物离子导电电解液传导到阳极，在那里它们形成分子氧。在这项研究中，我们将研究由钙钛矿氧化物和金属/双金属氮化物/氧氮化物组成的复合阴极系统，并研究这些相之间的协同作用。采用复合体系的基本原理是钙钛矿型氧化物相将催化H2O的分解并提供氧离子和电子电导，而氮化物/氮氧化物相将促进氮气的活化并提供氮离子的迁移率。据我们所知，这种协同效应以前从未报道过。我们的方法是研究高温电催化合成氨的概念，并为此目的研究氧化物/氮化物复合阴极，包括材料合成、非原位/原位/操纵性表征和电催化活性测试的迭代过程。该项目所获得的知识将有助于开辟一条由氮气和水合成氨的新路线。它还将帮助开发类似的电解/电催化电池，用于环境重要的过程，如电催化还原NOx和共同电解二氧化碳和水以生产合成气。除了对高温电催化氨合成文献的潜在贡献外，拟议的研究还具有在电催化、材料合成、表面化学和动力学方面提供有价值的见解的巨大潜力。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。

This project focuses on a strategy for producing ammonia from N2 and H2O electrocatalytically at atmospheric pressure. The conventional route for ammonia (NH3) production is the Haber-Bosch (HB) process, which involves converting nitrogen and hydrogen through a thermo-catalytic reaction at high temperatures and high pressures. The demand for ammonia has been continuously increasing due to its widespread use in several industrial sectors including agriculture (approximately 80% of the produced ammonia is used to make fertilizer), transportation, pharmaceuticals, explosives, as well as the energy sector as a promising indirect hydrogen storage medium. Considering the increasing demand for NH3 and the highly energy-intensive nature of the conventional process with significant CO2 emissions, a cleaner and less energy-intensive alternative will have a significant economic and environmental impact. In addition, this project has the potential to provide new insights into the material synthesis and characterization, the mechanistic steps and the electro-catalytic phenomena, which can be translated to other catalytic and electrocatalytic systems for environmentally-important processes such as electrocatalytic reduction of NOx and CO2 electrolysis. Research activities proposed here will be integrated with established education and outreach programs at the Ohio State University with the ultimate goal of increasing student participation, retention and graduation in STEM fields. The overall goal of the project is to develop highly active and selective cathode electro-catalysts for the high-temperature electrosynthesis of ammonia in solid oxide electrolysis cell (SOEC)-type reactors. The high-temperature (400-600 degrees C) electrocatalytic ammonia synthesis will involve dissociation of H2O to form H+ and O2- and the electrocatalytic activation of N2, followed by reaction with H+ to form NH3. In this scheme, O2- ions are conducted through the oxide ion conducting electrolyte to the anode, where they form molecular oxygen. In this study, we will examine a composite cathode system which is composed of perovskite oxides and metallic/bimetallic nitride/oxynitrides and we will investigate the synergy between these phases. The rationale of using a composite system is that the perovskite oxide phase will catalyze the H2O dissociation and provide oxide ion and electronic conductivity while the nitride/oxynitride phase will promote the N2 activation and provide nitrogen ion mobility. To the best of our knowledge, such a synergistic effect has never been reported before. Our approach to study the high-temperature electrocatalytic production of ammonia concept and to investigate an oxide/nitride composite cathode for this purpose will involve an iterative process of material synthesis, ex-situ/in-situ/operando characterization and electrocatalytic activity tests. The knowledge gained in this project will help open up a new route ammonia synthesis from N2 and H2O. It will also help develop similar electrolysis/electrocatalytic cells for environmentally-important processes such as electrocatalytic reduction of NOx and co-electrolysis of CO2 and H2O for syngas production. In addition to its potential contribution to the high-temperature electrocatalytic ammonia synthesis literature, the proposed study has significant potential to provide valuable insights in electrocatalysis, materials synthesis, surface chemistry and kinetics.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.