Cu–Ni materials prepared by mechanical milling: Their properties and electrocatalytic activity towards nitrate reduction in alkaline medium

CuxNi1−x materials (0 ≤ x ≤ 100) were elaborated by high-energy ball milling. The milling conditions were optimized using the composition Ni80Cu20. Utilizing a ball-to-powder mass ratio of 2 and a milling time of 6 h, one can obtain nanocrystalline Ni80Cu20 alloys (crystallite size <50 nm) with a good milling yield (>95%) and with a very low Fe contamination (<1 at.%). CuxNi1−x alloys prepared under optimized milling conditions were used as electrode materials for the electrochemical reduction of nitrate and nitrite in alkaline medium. The analyses of the products formed during the nitrate electrolysis revealed the formation of only ammonia and nitrite ions. The increase in Ni content in the materials resulted in increasing the selectivity for ammonia formation. On the other hand, the nitrate destruction rate increased as the Cu content in the materials was raised, attaining 9.8 × 10−4 mol cm−2 h−1 for pure Cu. This confirms the higher electrocatalytic activity of Cu with respect to Ni for nitrate reduction in alkaline solutions.