Optimization of Sm-Co Alloy Electrodeposition: Influence of Electrolyte pH, L-Arginine Concentration and Samarium Precursor Content

This study investigates and optimizes the potentiostatic electrodeposition of samarium-cobalt (Sm-Co) alloy coatings on copper substrates from aqueous electrolytes, utilizing L-arginine as an environmentally friendly complexing agent. The interdependent effects of electrolyte pH (1.0–4.0), L-arginine concentration (0.05–0.15 M), and initial samarium oxide (Sm2O3) precursor concentration (0.075–0.1 M) were evaluated across cathodic potentials ranging from −1.1 V to −1.8 V vs. Ag/AgCl. Increasing the pH from 1.0 to 4.0 enhanced samarium incorporation, reaching a peak value of 38 at.% Sm at pH 4.0. Although a low L-arginine concentration (0.05 M) yielded maximum local samarium content (58 at.%), incomplete metal complexation resulted in severe microcracking. Higher ligand concentrations (0.1–0.15 M, where L denotes L-arginine) ensured full complexation into [CoL]2+ and [Sm(HL)]3+ species, shifting cobalt reduction potentials negatively and producing compact, crack-free coatings at potentials between −1.6 V and −1.8 V. Strong cathodic polarization triggered intense hydrogen evolution, leading to local alkalization, hydroxide (Sm(OH)3) precipitation, increased oxygen incorporation (up to 86%), and current efficiency loss. Achieving uniform, crack-free Sm-Co coatings with high samarium content requires an electrolyte pH of 3.2–4.0 and an L-arginine concentration of at least 0.1 M.