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

本项目重点研究常压下由N2和H2O电催化制氨的策略。氨（NH3）生产的传统途径是Haber-Bosch （HB）工艺，该工艺涉及在高温高压下通过热催化反应转化氮和氢。由于氨在几个工业部门的广泛应用，包括农业（大约80%的氨被用于制造肥料）、运输、制药、炸药以及能源部门作为一种有前途的间接储氢介质，对氨的需求一直在不断增加。考虑到对NH3的需求不断增加，以及传统工艺的高能耗性质和大量的二氧化碳排放，一种更清洁、更低能耗的替代方案将产生重大的经济和环境影响。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，这些见解可以转化为其他催化和电催化系统，用于对环境重要的过程，如电催化还原NOx和CO2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项目相结合，最终目标是提高学生在STEM领域的参与度、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池（SOEC）型反应器中高温电合成氨的高活性和选择性阴极电催化剂。高温（400-600℃）电催化合成氨将H2O解离生成H+和O2-，电催化活化N2，再与H+反应生成NH3。在这个方案中，氧离子通过氧化离子导电电解质传导到阳极，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。使用复合体系的基本原理是钙钛矿氧化物相将催化H2O解离并提供氧化离子和电子导电性，而氮化物/氧氮化物相将促进N2活化并提供氮离子的流动性。据我们所知，这种协同效应以前从未被报道过。我们研究高温电催化生产氨的概念，并为此目的研究氧化物/氮化物复合阴极的方法将涉及材料合成、非原位/原位/operando表征和电催化活性测试的迭代过程。本项目所获得的知识将有助于开辟一条由N2和H2O合成氨的新路线。它还将有助于开发类似的电解/电催化电池，用于对环境重要的过程，如电催化还原氮氧化物和用于合成气生产的二氧化碳和水的共电解。除了对高温电催化合成氨文献的潜在贡献外，该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见解的重大潜力。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。

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.