Understanding the Electrocatalytic Interface for Ambient Ammonia Synthesis

Electrochemical reduction of N-2 to NH3 under ambient conditions can enable an alternative approach for sustainable, distributed production of NH3 when powered by renewable electricity. However, the development of such a process has been hindered by the lack of efficient electrocatalysts for the N-2 reduction reaction (NRR) because of the barrier for N-2 activation and the competing hydrogen evolution reaction (HER). Here, we highlight some mechanistic insights into the electrode-electrolyte interface for NH3 electrosynthesis, where the NRR and HER compete for the available protons, electrons, and catalytic surface sites. The competition even dominates the electrokinetics of NRR, so that the NRR activity typically declines at relatively higher overpotentials. Methods are thus proposed to mitigate the competition from the HER and boost the NRR activity and selectivity, including optimizing the electrolyte, revealing structure activity-relationships for rational catalyst design, and developing gas-diffusion-electrode flow cells with a controlled local liquid/gas environment for NRR electrolysis.