The effect of organic additives in electrodeposition of Co from an amide-type ionic liquid

The effect of organic additives, coumarin and thiourea (TU), on the electrodeposition of cobalt (Co) was investigated in an amide-type ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA), containing Co(TFSA)₂ as a Co source. In case of addition of coumarin, the deposition potential of Co shifted to the positive side while there was no change in the coordination environment of Co²⁺. However, the surface morphology was changed by addition of coumarin, suggesting the specific adsorption of coumarin on the surface of electrode. On the other hand, the deposition potential of Co shifted to the more positive side by addition of TU, probably due to the change in the coordination environment of Co²⁺ from [Co(TFSA)₃]⁻ to [Co(TU)₄]²⁺. The diffusion coefficient of [Co(TU)₄]²⁺ was determined as 7.2 × 10⁻⁸ cm² s⁻¹ at 27 °C by chronoamperometric method. The surface morphology of electrodeposit obtained from the electrolyte with TU was flat and less granular as compared to that without TU.