Co-deposition of Co, Ni, and Ru from the choline chloride-ethylene glycol deep eutectic solvent

Abstract

In this research, we explore the co-deposition of Co, Ni, and Ru from ethaline – a mixture of choline chloride and ethylene glycol in a 1:2 molar ratio. Co, Ni, and Ru were co-deposited from ethaline-based solutions containing their respective chloride salts, with LiCl and H₂SO₄ added in some cases. Deposition was carried out at constant potentials ranging from -1.00 V to -1.34 V, at 70°C, for up to 4 h. The morphology of the resulting deposits was examined using scanning electron microscopy, while their composition was analyzed by energy-dispersive X-ray spectroscopy and X-ray diffraction. The obtained Co-Ni deposit morphologies ranged from mostly smooth, dense layers to platelets and dendritic formations, influenced by the presence of H₂SO₄ and LiCl in the solution. In contrast, the addition of Ru resulted in a more porous, netlike deposit. Composition analyses confirmed the presence of all three target elements but showed a significant reduction in Co content in deposits obtained from multi-component baths. Selected Co-Ni-Ru deposits were tested as hydrogen evolution catalysts in 1.0 M KOH and 0.5 M H₂SO₄, where they showed good activity.