Compositional Control of Electrodeposited Co-Ni-Cu Thin Films and Their Behavior in Nitrate Reduction

Cobalt-nickel-copper alloys were electrodeposited over a range of current density and with three different aqueous electrolytes having variable metal ion ratios, in order to examine changes in the deposit composition and to use them as cathodes for nitrate electrolysis. The alloys were electrodeposited galvanostatically from a citrate electrolyte onto rotating cylindrical steel substrates. The electrodeposition process exhibited anomalous codeposition behavior, favoring Co reduction over Ni and Cu. These electrodeposits were then used to examine their ability to reduce nitrate in simulated wastewater with 50 mg-N/L of NO₃^-, sodium chloride, and sodium sulfate. Nitrate conversion and selectivity were characterized after electrolysis in a single-compartment cell with the alloys serving as the working electrode. Despite co-evolving hydrogen, the electrodeposited alloys were effective at generating both N₂ at high electrolysis current densities and ammonia species at lower values, with the deposit composition also affecting the conversion and products. It is the first demonstration of using Co-Ni-Cu ternary alloys for nitrate reduction.