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

Abstract

Electrochemically converting waste nitrate (NO₃⁻) into ammonia (NH₃) is a green route for both wastewater treatment and high‐value‐added ammonia generation. However, the NO₃⁻‐to‐NH₃ reaction involves multistep electron transfer and complex intermediates, making it a grand challenge to drive efficient NO₃⁻ electroreduction with high NH₃ selectivity. Herein, an in‐operando electrochemically synthesized Cu₂O/NiO heterostructure electrocatalyst is proven for efficient NH₃ electrosynthesis. In situ Raman spectroscopy reveals that the obtained Cu₂O/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 NH₃ electrosynthesis. The orbital hybridization calculations further identify that Cu₂O is beneficial for NO₃⁻ adsorption, and NiO could promote the desorption of NH₃, forming an excellent tandem electrocatalyst. Such a tandem system leads to NH₃ Faradaic efficiency of 95.6%, a super‐high NH₃ selectivity of 88.5% at −0.2 V versus RHE, surpassing most of the NH₃ electrosynthesis catalysts at an ultralow reaction voltage.