Catalyst-free, electrolytic synthesis of ammonia from nitrogen and water by atmospheric-pressure plasma processes

One of the most well-known chemical processes is the synthesis of ammonia by the Haber-Bosch process. However, there are several drawbacks including the high pressure and high temperatures required and the dependence on hydrogen gas which comes from steam-methane reforming and leads to a large carbon footprint. Among the various alternative approaches being studied, electrolytic approaches that can be integrated with renewable sources such as solar and wind and operate near ambient conditions are the most attractive. Unfortunately, to date, these methods have suffered from low yields and selectivities associated with the catalyst and their high overpotentials and preference for the hydrogen evolution reaction.
In this talk, I will present a new electrolytic approach to ammonia synthesis from nitrogen and water based on non-equilibrium, atmospheric-pressure plasmas in contact with water surfaces. Distinctly, nitrogen is reduced without a catalyst by the unique interactions of the plasma and water. Specifically, electrons in the plasma potentially excite or even dissociate the nitrogen molecule in the gas phase, and solvate to produce one of the strongest reducing agents known. Remarkably, we find that for certain configurations and certain processing conditions, ammonia is synthesized with 100% charge-transfer (faradaic) efficiency. To make the process continuous and potentially overcome mass transport issues, we have recently also developed a plasma-droplet reactor in which water droplets flow through a plasma. Studies to reveal key reaction intermediates and potential reaction mechanisms in support of results in both reactors will be discussed.