Hawtof Ryan, Ghosh Souvik, Guarr Evan, Xu Cheyan, Mohan Sankaran R, Renner Julie Nicole
Department of Chemical and Biomolecular Engineering, Case Western Reserve University, Cleveland, OH, USA.
Sci Adv. 2019 Jan 11;5(1):eaat5778. doi: 10.1126/sciadv.aat5778. eCollection 2019 Jan.
There is a growing need for scalable ammonia synthesis at ambient conditions that relies on renewable sources of energy and feedstocks to replace the Haber-Bosch process. Electrically driven approaches are an ideal strategy for the reduction of nitrogen to ammonia but, to date, have suffered from low selectivity associated with the catalyst. Here, we present a hybrid electrolytic system characterized by a gaseous plasma electrode that facilitates the study of ammonia formation in the absence of any material surface. We find record-high faradaic efficiency (up to 100%) for ammonia from nitrogen and water at atmospheric pressure and temperature with this system. Ammonia measurements under varying reaction conditions in combination with scavengers reveal that the unprecedented selectivity is achieved by solvated electrons produced at the plasma-water interface, which react favorably with protons to produce the key hydrogen radical intermediate. Our results demonstrate that limitations in selectivity can be circumvented by using catalyst-free solvated electron chemistry. In the absence of adsorption steps, the importance of controlling proton concentration and transport is also revealed.
在环境条件下，对依赖可再生能源和原料的可扩展氨合成的需求日益增长，以取代哈伯-博施法。电驱动方法是将氮还原为氨的理想策略，但迄今为止，一直受到与催化剂相关的低选择性的困扰。在这里，我们展示了一种混合电解系统，其特征在于气态等离子体电极，便于在没有任何材料表面的情况下研究氨的形成。我们发现，使用该系统在大气压和温度下从氮气和水中合成氨的法拉第效率达到了创纪录的高水平（高达100%）。在不同反应条件下结合清除剂进行的氨测量表明，前所未有的选择性是由等离子体-水界面产生的溶剂化电子实现的，这些电子与质子发生有利反应，产生关键的氢自由基中间体。我们的结果表明，通过使用无催化剂的溶剂化电子化学可以规避选择性方面的限制。在没有吸附步骤的情况下，还揭示了控制质子浓度和传输的重要性。
