Tuning the Acid Hardness Nature of Cu Catalyst for Selective Nitrate‐to‐Ammonia Electroreduction

Electrocatalytic nitrate reduction reaction (NO₃RR) in alkaline electrolyte presents a sustainable pathway for energy storage and green ammonia (NH₃) synthesis. However, it remains challenging to obtain high activity and selectivity due to the limited protonation and/or desorption processes of key intermediates. Herein, we propose a strategy to regulate the acid hardness nature of Cu catalyst by introducing appropriate modifier. Using density functional theory calculations, we firstly identified that the BaO-modified Cu showed optimal Gibbs free energies for key NO₃RR steps, including the protonation of *NO and the desorption of *NH₃. Experimentally, the BaO-modified Cu catalyst exhibited 97.3 % Faradaic efficiency (FE) for NH₃ with a yield rate of 356.9 mmol h^-1 g_cat ^-1. It could also maintain high activity across a wide range of applied potentials and nitrate substrate concentrations. Detailed experimental and theoretical studies revealed that the Ba species could modulate the local electronic states of Cu, enhance the electron transfer rate, and optimize the adsorption/protonation/desorption processes of the N-containing intermediates, leading to the excellent catalytic performance for NO₃ ^--to-NH₃.