Electrocatalysis of Nitrate Reduction at Copper‐Nickel Alloy Electrodes in Acidic Media

Abstract The cathodic reduction of NO$\rm{ {_{3}^{-}}}$ in 1.0 M HClO4 is investigated by voltammetry at pure Ni and Cu electrodes, and three Cu‐Ni alloy electrodes of varying composition, all configured as rotated disks. Voltammetric data obtained using these hydrodynamic electrodes demonstrate significantly improved activity for NO$\rm{ {_{3}^{-}}}$ reduction at Cu‐Ni alloy electrodes as compared to the pure Ni and Cu electrodes. This observation is explained on the basis of the synergistic benefit of different surface sites for adsorption of H‐atoms, generated by cathodic discharge of H+ at Ni‐sites, and adsorption of NO$\rm{ {_{3}^{-}}}$ at Cu‐sites on these binary alloy electrodes. Koutecky‐Levich plots indicate that the cathodic response for NO$\rm{ {_{3}^{-}}}$ at a Cu75Ni25 electrode corresponds to an 8‐electron reduction, which is consistent with production of NH3. In comparison, the cathodic response at Cu50Ni50 and Cu25Ni75 electrodes corresponds to a 6‐electron reduction, which is consistent with production of NH2OH. Flow injection data obtained using Cu50Ni50 and Cu25Ni75 electrodes with 100‐μL injections exhibit detection limits for NO$\rm{ {_{3}^{-}}}$ of ca. 0.95 μM (ca. 95 pmol) and 0.60 μM (ca. 60 pmol), respectively.