Nitrogen electrochemically reduced to ammonia with hematite: density-functional insights

Abstract

Licht et al. (Science, 2014, 345, 637) recently proposed a procedure to synthesize NH₃ from N₂ and by steam electrolysis in molten hydroxide suspensions of nano-Fe₂O₃. This highly exciting investigation undoubtedly boosts the hope of the CO₂-free and low-cost ammonia industry. To provide insights at the atomistic level into the reduction process of N₂, we have carried out a density-functional study on the electrochemical formation of NH₃ molecules on hematite(0001) surfaces. By considering associative and dissociative mechanisms, we have identified a reaction path that requires an applied bias of −1.1 V to allow the proton transfer processes to occur downhill. The most energy-demanding step is the addition of the first proton to the adsorbed molecular nitrogen. The computed bias is in good agreement with experimental electrolysis potentials that activate the electric current.