Fe–Co coatings electrodeposited from eutectic mixture of choline chloride-urea: Physical characterizations and evaluation as electrocatalysts for the hydrogen evolution reaction

Abstract Fe–Co coatings were electrodeposited on Cu substrates from a choline chloride-urea eutectic solution. The influence of Fe and Co content on the magnetic, morphological, and electrocatalytic properties of the electrodeposits was duly studied. The coercivity and quadrature of the magnetic hysteresis curves revealed that all coatings had soft magnetic properties that varied with the coating composition. A hyperfine magnetic field between 36 and 38 T in their Mossbauer spectra indicated the formation of Fe–Co alloy in the samples Fe87Co13, Fe64Co36, and Fe44Co56. All coatings with Fe content higher than 25% showed magnetic texture along their growth axis with orientation angles ranging from θ = 5.1 to 42.8∘. The Fe, Co, and Fe–Co coatings showed good electrocatalytic performance for the hydrogen evolution reaction, with mainly the Fe-rich coatings presenting the lowest values of overpotential. Remarkably, an Fe coating afforded a current density of 10 cm−1 at a low overpotential of 89.2 mV, as well as exhibiting a small Tafel slope of 44.6 mV dec−1 in 0.5 mol L−1 NaOH. The results showed that the use of choline chloride-urea eutectic solution provides a promising and ecological strategy for the production of Fe–Co coatings since it is not necessary to add other chemicals besides the corresponding metallic salts.