Dinitrogen fixation by alkali and alkaline earth hydride composites under plasma

Abstract

The development of alternative methods for sustainable dinitrogen (N₂) fixation to ammonia (NH₃) is a cutting-edge research area. The presence of external stimuli, such as non-thermal plasma, can boost the activation of the inert N₂ molecules under ambient temperatures and pressures, thereby generating value-added products such as NH₃ or other nitrogen-containing compounds. Binary alkali metal hydrides such as NaH and KH have recently shown intriguing properties in the plasma nitrogen fixation process. Herein we report the different chemical behaviors of a series of hydride composites consist of potassium hydride (KH) and alkaline earth metal hydride (MgH₂, CaH₂, SrH₂, and BaH₂) under nitrogen plasma conditions. A nitrogen-relayed mechanism has been proposed to understand the different nitrogen fixation behaviors on these hydride composites. Under this scenario, KH is responsible for plasma N₂ fixation to form surface NH₂ species, which subsequently migrate and react with MgH₂, CaH₂, and SrH₂ to form N and NH species, respectively. This work enriches the plasma chemistry of metal hydrides, and provides a strategy to enhance the amounts of fixed nitrogen of single hydride material under nitrogen plasma conditions.