LAUSR

: Developing effective electrocatalysts for nitrate reduction to ammonia is paramount for ammonia synthesis while addressing the water pollutant issue. Identifying the active structure and its correlation with catalytic behavior during the reaction process is essential and challenging for the rational design of advanced electrocatalysts. Herein, starting from Cu 2 O particles with controllable crystal facets, the electrochemically reconstituted Cu/ Cu 2 O was fabricated as a suitable catalytic system, and the relationship between the chemical state of copper and product selectivity in the nitrate reduction reaction was studied. At − 0.9 V versus reversible hydrogen electrode, the oxide-derived Cu 0 (OD-Cu) cube achieved a high ammonia Faradaic efficiency of 93.9% and productivity of up to 219.8 μ mol h − 1 cm − 2 , surpassing those of most Cu-based catalysts. In situ Raman analysis, well-designed pulsed electrolysis experiments, and theoretical calculations showed that ammonia was preferentially produced on OD-Cu at high reduction potentials and the presence of the Cu/Cu 2 O interface favored nitrite formation at low reduction potentials. The high ammonia selectivity of the OD-Cu cube originated from the enhanced adsorption of nitrate and lower reaction barrier of the potential-determining step ( * NH 3 → NH 3 ). This work presents an effective strategy to boost electrocatalysis and offers an insight into the real active phase and corresponding catalytic behavior of Cu-based electrocatalysts.