Catalyst-Free, Electrolytic Synthesis of Ammonia from Nitrogen and Water By Plasma-Produced Solvated Electrons

Abstract

Ammonia which is a precursor to fertilizers and food and is one of the most important chemicals in the world is currently synthesized on a large scale by the Haber-Bosch (H-B) process. Recent research has been aimed at developing alternative approaches to synthesizing ammonia to address several issues associated with the H-B process: 1) the very high pressures and high temperatures which lead to enormous capitals costs, 2) the need for hydrogen gas which comes from steam-methane reforming and contributes to high energy costs and environmental impact through greenhouse gas emissions, and 3) the incompatibility with renewable sources of energy that could lower energy costs and environmental impact while also offering more localized, point-of-use sources of ammonia. Here, we report a hybrid electrochemical system to produce ammonia where one of the metal electrodes is replaced by a plasma (gas discharge). Similar to more typical electrochemical systems, ammonia synthesis is carried out at ambient conditions and only requires electricity. However, the interaction of a plasma and water leads to the formation of solvated electrons, one of the strongest reducing agents known with a reduction potential of ~-2.8 V. Production rates and selectivity (i.e. charge-transfer efficiency) were determined as a function of various process parameters including current, time, and electrolyte composition. We will also discuss a potential reaction mechanism based on the observed results.