Electrochemical hydrogenation of nitrogen to ammonia under ambient conditions in a suspended dual-catalyst system†

Abstract

Electrocatalytic hydrogenation provides a sustainable method and green route to convert atmospheric nitrogen N₂ into ammonia NH₃ under mild conditions but is still challenged with the issues of low working current density and low faradaic efficiency. Herein, a suspended electrocatalytic dual-catalyst system was designed to realize the nitrogen hydrogenation into ammonia with high faradaic efficiency and high working current density, which is often thought to be rather difficult in aqueous electrolysis. The electrochemical system uses a soluble polyoxometalate of silicotungstic acid as an electron captor and a suspended noble-metal catalyst Ru/TiO₂ as the nitrogen fixation catalyst, so that the catalyst particles can be detached from the electrode, which is quite different from common electrochemical systems. Because the nitrogen fixation catalyst is free from the electrode, no current flows through the catalyst and even a non-conductive catalyst can be used, so that the suspended electrochemical system can provide a rather large opportunity and maneuverability for enhancing the nitrogen fixation process.