Characterization and electrodeposition mechanism of Ni–Mo coatings from self-regulating electrolyte

Electrochemical Ni–Mo coatings were obtained on a low-carbon steel substrate using a stable, environmentally safe, self-regulating electrolyte containing 0.2 M NiCl 2 , 0.3 M Na 3 C 6 H 5 O 7 , and SrMoO 4 (saturated). The effects of electrolyte pH, temperature, deposition current density, and hydrodynamic conditions on chemical composition and morphology of the coatings were studied. It was established that the addition of ammonia to the electrolyte contributes to the deposition of a more uniform, globular, nonporous coatings morphology. The effect of ammonia on the formation mechanism of coatings was substantiated. The stages of deposition and the limiting stage of the formation of Ni–Mo coatings from citrate-ammonia electrolytes, which involves the chemical reduction of molybdenum oxide (IV) to molybdenum, were determined using cyclic voltammetry. • Ni–Mo coatings were deposited from a stable, environmentally safe and self-regulating electrolyte. • Electrolysis regimes have been worked out. • Following chemical reaction of the reduction of molybdenum (IV) oxide to adsorbed molybdenum is limiting reaction. • Scheme of deposition of nickel-molybdenum coatings was constructed.