Enhancing corrosion resistance of electrodeposited Ni-P alloy coatings via glycine-modified

Nickel‑phosphorus (Ni-P) alloys have been widely adopted in engineering applications owing to their high hardness, excellent wear and corrosion resistance, making them a viable and more environmentally friendly alternative to hard chromium coatings, which face stringent environmental regulations. The electrodeposition technique for producing Ni-P alloys has attracted considerable attention due to its cost efficiency and suitability for large-scale manufacturing. In this study, we present a sustainable electrodeposition strategy that eliminates boric acid and employs glycine—a biodegradable, non-toxic amino acid—as the sole complexing agent to produce high-performance Ni-P coatings. Key deposition parameters, including temperature, current density and pH, were systematically optimized based on corrosion resistance performance. Electrochemical tests confirmed that glycine effectively complexes with Ni²⁺ and reduces the deposition kinetics. AFM revealed that the incorporation of glycine reduces the surface roughness (R_a) from 29.8 nm to 19.8 nm, promoting the formation of a uniform and dense coating structure, which helps alleviate stress corrosion. XPS and TOF-SIMS analyses indicated that the coatings produced in the glycine-modified system are enriched with Ni-O, Ni–OH, and phosphate species, key components of a protective passive layer that acts as an effective barrier against corrosion. EIS and Tafel measurements conducted in 3.5 wt% NaCl solution demonstrated that the glycine-modified Ni-P coatings exhibit a significant increase in charge transfer area resistance for corrosion from 1348 to 3584 Ω cm² and a decrease in corrosion current density from 18.3 to 5.5 μA/cm². The synergistic role of glycine in refining the microstructure, enhancing phosphorus incorporation, and reinforcing the passive film establishes this approach as a green and efficient strategy for producing corrosion-resistant coatings.