Atomic-scale redox-potential-mediated engineering of 0D/2D Cu–Cu 2 O/MO x (OH) y heterojunctions for efficient nitrate electroreduction to ammonia

The precise construction of zero-dimensional/two-dimensional (0D/2D) heterojunctions is often hindered by interfacial lattice mismatches and uncontrolled phase transitions, limiting their efficacy in electrocatalysis. Herein, we report a widely applicable redox-potential-mediated strategy for the atomically defined fabrication of 0D/2D Cu-Cu₂O/MO _x (OH) _y heterojunctions (M = Ni, Fe, Mn, Co, Cr). This approach leverages the inherent differences in standard reduction potentials between Cu and transition metals to drive selective oxidation and ultrasound-assisted hydrolysis of pre-synthesized CuM alloy nanoparticles. This process results in situ phase separation, forming epitaxially embedded Cu-Cu₂O nanoparticles within ultrathin MO _x (OH) _y nanosheets. As a proof of concept, the Cu-Cu₂O/Ni(OH)₂ heterojunction exhibits exceptional performance in the electrocatalytic nitrate reduction reaction (eNITRR), achieving an outstanding ammonia yield rate of 12,974.5 µg cm^-2 h^-1 (at a mass loading of 1 mg cm^-2) and a Faradaic efficiency of 98.15%, ranking it among the high-performing catalysts reported to date. Mechanistic studies reveal a synergistic interfacial effect: Cu-Cu₂O promotes nitrate adsorption and activation, while Ni(OH)₂ selectively cleaves H₂O to generate reactive *H species, thereby accelerating the hydrogenation steps. This redox-guided synthesis provides a useful framework for the atomic-scale engineering of heterointerfaces, paving the way for advanced electrocatalysts in sustainable nitrogen valorization and beyond.