Cube-Cu ₂ O/CoAl-Layered Double Hydroxide for Electrocatalytic Nitrate Reduction to Ammonia: Spontaneous Nitrate Deoxygenation and Consecutive Hydrogenation

The electrochemical nitrate reduction reaction (NO 3 RR) offers an attractive pathway for ammonia synthesis and nitrate remediation. However, its efficiency is constrained by sluggish proton-coupled electron transfer and strong competition from the hydrogen evolution reaction (HER), both of which critically depend on the formation and transfer of active hydrogen (*H) intermediates. In this work, Cube-Cu 2 O/MAl-layered double hydroxides (M = Ni, Co, Mg) are constructed by a wet chemical reduction strategy. Comprehensive in situ spectroscopy and theoretical calculations demonstrate that varying the M 2+ cations in the MAl-LDH support can regulate the microenvironment of the Cu 2 O phase, among which the Cu 2 O on CoAl-LDH exhibits the fastest kinetics for driving the initial NO 3 − -to-NO 2 − step to proceed spontaneously. Moreover, the interfacial water structure is also tuned by the CoAl-LDH support, endowing optimal kinetics for water activation and proton supply. This synergistic effect between Cu 2 O and CoAl-LDH boosts the overall NO 3 RR performance, achieving a Faradaic efficiency of 98.42% and a high ammonia yield rate of 37.4 mg cm −2 h −1 at −0.48 V vs RHE, thereby outperforming most reported state-of-the-art electrocatalysts. Our findings offer fundamental insights into interfacial design for steering reaction pathways toward efficient ammonia synthesis.