Optimization of electrolytic expandable graphite / nickel-cobalt phosphite coating parameters

This thesis investigates the production of nickel-cobalt phosphide coatings on expandable graphite using the electrolysis method and the optimization of coating parameters. Electrolysis was chosen due to its ability to precisely control coating thickness and composition. Current density, stirring rate, and coating duration were evaluated for their effects on coating quality, surface morphology, and electrochemical performance. Experiments showed that low current density (0.5 mA/cm²) and short duration (15 minutes) increased crystallinity to 86.9%, forming homogeneous crystal structures. High current density (1.59 mA/cm²) and long duration (105 minutes) reduced crystallinity to 3.9%, resulting in amorphous structures. Electrolyte concentration supports ion mobility, optimizing crystal formation. XRD analyses revealed distinct phase structures at low current density, while BET analyses indicated that high-crystallinity coatings offer a wide surface area and regular pore structure. SEM and microhardness analyses confirmed the high performance of optimized coatings. Findings highlight that low current and short duration combinations are critical for achieving high crystallinity and mechanical strength in electrochemical coatings.