AUTHOR=To Dung T. , Park Sun Hwa , Kim Min Joong , Cho Hyun-Seok , Myung Nosang V. 

TITLE=Effects of NH4+/citrate complexing agent ratio on Ni–Mo and Ni–Mo–O electrodeposits from ammonium citrate baths

JOURNAL=Frontiers in Chemistry

VOLUME=Volume 10 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2022.942423

DOI=10.3389/fchem.2022.942423

ISSN=2296-2646

ABSTRACT=To understand the effect of complexing agents (i.e., ammonium and citrate) in nickel-molybdenum electrodeposition, we calculated the concentration of various Ni and Mo species as a function of pH and initial concentration of metal ions and complexing agents.  Additionally, linear sweep voltammetry was systematically investigated to understand their effects on electrodeposition. Furthermore, Hull cell experiments were conducted to understand the effect of ammonium-to-citrate ratio to film compositions and morphology. The results indicated that Ni(NH3)32+ played a critical role in induced co-deposition mechanism of Ni-Mo alloys which involved the reduced Ni and absorbed H atoms.  Microstructure analysis of deposits indicated that they transition from smooth laminarly grown amorphous Ni-Mo-O composites to columnar metallic Ni-Mo alloys with globular structure as the ammonium-to-citrate molar ratio increases. The highest Mo content of alloys was as high as 19 at%, and up to 70 at% O was present in the composites.