Electrodeposited P-Doped CuNi Alloy from Deep Eutectic Solvent for Efficient and Selective Nitrate-to-Ammonia Electroreduction.

Electrochemical nitrate reduction reaction (NORR) offers a promising alternative for ammonia production using electricity generated from renewable energy sources. Active electrocatalysts with high selectivity and high yield are required to selectively catalyze NORR to ammonia. Here, P-doped CuNi alloy thin films are electrodeposited from a deep eutectic solvent of choline chloride-ethylene glycol (ChCl/EG). The P-CuNi produces 1616.94 µg h cm of ammonia at -0.55 V (V versus reversible hydrogen electrode), with a Faradaic efficiency of 98.38% and ammonia selectivity of 97.84% at -0.25 V, much better than the P-Ni and P-Cu prepared under similar condition. The high ammonia production rate, Faradaic efficiency and selectivity are originated from high number of electrochemically active sites and more facile kinetics. Mechanistic study and density functional theory calculation proves that P-CuNi exhibits higher conductivity and more facile NO adsorption compared to P-Ni and P-Cu, induced by the electron interaction. Characterizations after NORR cycling show that the crystallinity of P-CuNi decreases, with the content of divalent metal ions increases at the surface. The P-CuNi is an active and stable material to electrocatalyze NORR to ammonia in neutral aqueous solutions.