Electrocatalytic synthesis of ammonia by surface proton hopping

Abstract

Highly efficient ammonia synthesis at a low temperature is desirable for future energy and material sources. We accomplished efficient electrocatalytic low-temperature ammonia synthesis with the highest yield ever reported. The maximum ammonia synthesis rate was 30 099 μmol g_cat^-1 h^-1 over a 9.9 wt% Cs/5.0 wt% Ru/SrZrO₃ catalyst, which is a very high rate. Proton hopping on the surface of the heterogeneous catalyst played an important role in the reaction, revealed by <i>in situ</i> IR measurements. Hopping protons activate N₂ even at low temperatures, and they moderate the harsh reaction condition requirements. Application of an electric field to the catalyst resulted in a drastic decrease in the apparent activation energy from 121 kJ mol^-1 to 37 kJ mol^-1. N₂ dissociative adsorption is markedly promoted by the application of the electric field, as evidenced by DFT calculations. The process described herein opens the door for small-scale, on-demand ammonia synthesis.