Electrocatalytic nitrate (NO₃⁻) reduction to ammonia (NH₃) offers a viable approach for sustainable NH₃ production and environmental denitrification. Copper (Cu) possesses a distinctive electronic structure, which can augment the reaction kinetics of NO₃⁻ and impede hydrogen evolution reaction (HER), rendering it a promising contender for the electrosynthesis of NH₃ from NO₃⁻. Nevertheless, the role of Cu₂O in copper-based catalysts still requires further investigation for a more comprehensive understanding. Herein, the Cu₂O/Cu(OH)₂ heterostructures are successfully fabricated through liquid laser irradiation using CuO nanoparticles as a precursor. Experimental and theoretical researches reveal that Cu₂O/Cu(OH)₂ heterostructure exhibits enhanced electrocatalytic performance for NO₃⁻ to NH₃ because Cu(OH)₂ promotes electron transfer and reduces the valence state of Cu active site in Cu₂O. At −0.6 V (vs. reversible hydrogen electrode (RHE)), the NH₃ yield reaches its maximum at 1630.66 ± 29.72 μg·h⁻¹·mg_cat⁻¹, while the maximum of Faraday efficiency (FE) is 76.95% ± 5.51%. This study expands the technical scope of copper-based catalyst preparation and enhances the understanding of the electrocatalytic mechanism of NO₃⁻ to NH₃.