Influence of Positional Isomeric Spacers of Naphthalene Derivatives on Ni–W Alloy Electrodeposition: Electrochemical and Microstructural Properties

[Image: see text] Herein, Ni–W alloy matrixes were successfully fortified with two salen-type Schiff bases 1-((E)-(2-((E)-(2-hydroxynaphthalen-1-yl)methyleneamino)phenylimino)methyl)naphthalen-2-ol (OPD) and 1-((E)-(2-((E)-(2-hydroxynaphthalen-1-yl)methyleneamino)phenylimino)methyl)naphthalen-2-ol (PPD) as additives, of similar molecular structure but varied isomeric spacers, using a facile direct current electrodeposition technique. The resulting coatings from the additive-introduced reaction system were termed as Ni–W/OPD and Ni–W/PPD throughout the study. The deterioration process (0.5 M H(2)SO(4)), surface properties, elemental composition, functional groups, and structurs of the resultant coatings were analyzed by means of Tafel and electrochemical impedance spectroscopy, field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy, atomic force microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction (XRD). The bare Ni–W alloy deposition resulted in a loose microstructure with higher porosity density (12.2%), while that of additive-doped plating electrolytes resulted in a compact and dense microstructure with lesser porosity density (6.3%) and minimal porosity density (3.7%) as for Ni–W/OPD and Ni–W/PPD alloy coatings, respectively. Improved corrosion parameters presented superior corrosion characteristics of Ni–W alloy coatings from an additive (PPD)-induced bath, i.e., Ni–W/PPD. Synergetic adsorption of imine groups (N atoms), hydroxyl groups (O atoms), and aromatic electron clouds and reduction in steric hindrance produced by a larger isomeric spacer strengthened the surface adsorption of additives, yielding a fine nanocrystalline Ni–W coating with reduced porosity and well-refined grains, implying the outstanding shielding effect. Results of FESEM, AFM, and XRD analyses revealed a complete cohesion between two neighboring islands, resulting in a fine planar structure with minimal coating defects for Ni–W/PPD coatings, authenticating the corrosion parameters.