Room temperature electrodeposition of metallic magnesium from ethylmagnesium bromide in tetrahydrofuran and ionic liquid mixtures

The redox processes, nucleation-growth mechanisms and magnesium (Mg) speciation associated with the room temperature electrodeposition of metallic Mg on an aluminum (Al) electrode are described from mixed deposition media composed of 0.095 M ethylmagnesium bromide (EtMgBr)/tetrahydrofuran (THF) and 0.54 M ionic liquid including: 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate ([Py₁₄][FAP]), 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([Py₁₄][TFSI]), 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide ([Py₁₄][FSI]), 1-butyl-1-methylpiperidinium bis(trifluoromethylsulfonyl)imide ([Pip][TFSI]), ethyldimethylpropylammonium bis(trifluoromethylsulfonyl)imide ([N1123][TFSI]) and diethylmethyl (2-methoxyethyl) ammonium bis(trifluoromethylsulfonyl)imide ([DEME][TFSI]). Cyclic voltammetric results show a chemically reversible Mg/Mg²⁺ process in the case of [FAP]- and [TFSI]- based ionic liquids, but not for the [FSI]- based one, ascribed to ionic liquid dependent Mg speciation. Analysis of chronoamperometric data reveal that in the presence of [Py₁₄][FAP] and [Pip][TFSI], Mg nucleation follows a 3D instantaneous nucleation and diffusion controlled semi-spherical growth model. However, in the case of [Py₁₄][TFSI], [DEME][TFSI] and [N1123][TFSI], deviations from this model are evident. The influence of deposition parameters, such as current density and deposition time, on appearance, crystallite size and preferred orientation of Mg are also reported in a deposition medium containing 90% 1 M EtMgBr/THF and 10% ionic liquid (v/v ratio). [Py₁₄][FAP] was found to be the most favourable ionic liquid for electrodepositon of Mg.