Synergistic Active Phases of Transition Metal Oxide Heterostructures for Highly Efficient Ammonia Electrosynthesis

Abstract Electrochemically converting waste nitrate (NO 3 − ) into ammonia (NH 3 ) is a green route for both wastewater treatment and high‐value‐added ammonia generation. However, the NO 3 − ‐to‐NH 3 reaction involves multistep electron transfer and complex intermediates, making it a grand challenge to drive efficient NO 3 − electroreduction with high NH 3 selectivity. Herein, an in‐operando electrochemically synthesized Cu 2 O/NiO heterostructure electrocatalyst is proven for efficient NH 3 electrosynthesis. In situ Raman spectroscopy reveals that the obtained Cu 2 O/NiO, induced by the electrochemistry‐driven phase conversion, is the real active phase. This electronically coupled phase can modulate the interfacial charge distribution, dramatically lower the overpotential in the rate‐determining step and thus requiring lower energy input to proceed with the NH 3 electrosynthesis. The orbital hybridization calculations further identify that Cu 2 O is beneficial for NO 3 − adsorption, and NiO could promote the desorption of NH 3 , forming an excellent tandem electrocatalyst. Such a tandem system leads to NH 3 Faradaic efficiency of 95.6%, a super‐high NH 3 selectivity of 88.5% at −0.2 V versus RHE, surpassing most of the NH 3 electrosynthesis catalysts at an ultralow reaction voltage.