Sodium Substitution Effects on Ammonia Selectivity of Cu₃N Nanocrystals for Electrochemical Nitrate Reduction

Copper nitride (Cu₃N) nanocrystals are promising non-precious electrocatalysts for nitrate reduction due to their nitrogen-rich lattice and tunable electronic structure. Here, we demonstrate a ligand-assisted hot-injection synthesis of sodium-doped Cu₃N nanocrystals using sodium acetoacetate and sodium nitrate precursors to control Na incorporation. Structural and spectroscopic characterization confirms successful Na incorporation without phase decomposition, with Na-induced lattice distortions and electronic modifications at copper sites. Electrochemical testing in neutral aqueous nitrate electrolytes reveals a twofold increase in Faradaic efficiency for sodium-doped Cu₃N compared to undoped controls. UV-Vis assisted indophenol tests confirm selective NH₃ formation, while impedance spectroscopy and post-catalysis TEM and XPS analyses indicate enhanced charge transfer and surface reconstruction. These results highlight alkali cation exchange as a modular strategy to tune activity and selectivity in Cu₃N-based electrocatalysts.