Fe_xNi(_1-x) coatings electrodeposited from choline chloride-urea mixture: Magnetic and electrocatalytic properties for water electrolysis

Fe, Ni, and FexNi(1-x) coatings were successfully electrodeposited on Cu substrates from a choline chloride-urea eutectic solution without the addition of complexing agents. In addition, its magnetic properties and electrocatalytic performance for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) were fully investigated. X-ray diffraction and Mo spacing diaeresis ssbauer spectroscopy analyses characterized the formation of Fe-Ni alloys in the following coatings: Fe89Ni11, Fe69Ni31, Fe47Ni53, and Fe28Ni72. The magnetic measurements showed that all electrodeposits presented low coercivity, characterizing the coatings as soft magnetic materials. The Fe coating presented the best electrocatalytic performance for HER and OER in 0.5 mol L-1 NaOH and at 298.15 K. However, the Fe coating detached from the substrate when it was submitted to a long-term test. Among the FexNi(1-x) coatings, the Fe89Ni11 coating displayed the best performance for HER since it exhibited the lowest overpotential of 152 mV at an applied current density of 10 mA cm-2. For OER, the Fe69Ni31 and Fe47Ni53 were the best electrocatalysts, which presented the highest exchange current densities about of 7 x 10-4 mA cm-2 and overpotential values around 374 and 377 mV to provide 10 mA cm-2. Furthermore, the Ni and FexNi(1-x) coatings presented good stability in 120 h long term tests at 50 mA cm -2. Finally, the experimental results showed that the manufacture of electrocatalysts based on Fe, Ni and Fe-Ni coatings via electrodeposition conducted in the presence of choline chloride-urea is very promising and environmentally friendly process.