Electrocatalytic Hydrogenation of N₂ to NH₃ by MnO: Experimental and Theoretical Investigations

Abstract

NH₃ is a valuable chemical with a wide range of applications, but the conventional Haber-Bosch process for industrial-scale NH₃ production is highly energy-intensive with serious greenhouse gas emission. Electrochemical reduction offers an environmentally benign and sustainable route to convert N₂ to NH₃ at ambient conditions, but its efficiency depends greatly on identifying earth-abundant catalysts with high activity for the N₂ reduction reaction. Here, it is reported that MnO particles act as a highly active catalyst for electrocatalytic hydrogenation of N₂ to NH₃ with excellent selectivity. In 0.1 m Na₂SO₄, this catalyst achieves a high Faradaic efficiency up to 8.02% and a NH₃ yield of 1.11 × 10^-10 mol s^-1 cm^-2 at -0.39 V versus reversible hydrogen electrode, with great electrochemical and structural stability. On the basis of density functional theory calculations, MnO (200) surface has a smaller adsorption energy toward N than that of H with the *N₂ → *N₂H transformation being the potential-determining step in the nitrogen reduction reaction.