Electrodeposition of bismuth in a choline chloride/ethylene glycol deep eutectic solvent under ambient atmosphere

The electrochemical behavior of bismuth(III) is investigated under ambient atmosphere in the ethaline deep eutectic solvent (DES) that is obtained by mixing 1 mol eq. of choline chloride and 2 mol eq. of ethylene glycol using Bi(NO3)3 as the Bi(III) source. Cyclic voltammetry indicates that the presence of water adsorbed from the atmosphere reduces the viscosity of the DES, and hence facilitates the reduction of Bi(III) to Bi. The presence of high water contents, however, suppresses the solubility of Bi(NO3)₃ in the DES. Chronoamperometry experiments indicate that while the deposition of bismuth at a glassy carbon electrode involves with an overpotential-driven three dimensional instantaneous nucleation/growth process, the deposition of bismuth at the platinum, and nickel electrode involves with a progressive nucleation/growth. Crystalline bismuth films are deposited on Ni electrode by constant potential electrolysis. Scanning electron microscope images reveal that making the deposition potential more negative and/or increasing the temperature will reduce the deposited particle size. X-ray powder diffraction patterns suggest preferred orientation of the crystal growth. Bismuth coating can also be formed on copper substrate by galvanic displacement reaction between Bi(III) and Cu.