Ammonium chloride effects on bismuth electrodeposition in a choline chloride-urea deep eutectic solvent

The ammonium chloride effect on bismuth electrodeposition from choline chloride-urea deep eutectic solvent (DES) was investigated. Spectroscopic and thermal studies were performed on the latter in order to understand whether the addition of ammonium chloride affects the DES behavior; the results of the thermal study do not indicate any significant change except a small shift in the melting point of the DES when adding the ammonium salt (~+3 °C) and the modification of a cold crystallization peaks at low scan rate. The electrochemical behavior of bismuth was then studied by cyclic voltammetry in the deep eutectic solvent with different NH₄Cl content. Bismuth electrocrystallization was studied by chronoamperometry which has shown that the bismuth electrodeposition in studied conditions evolves with a three-dimensional progressive nucleation. SEM images show that grain size of bismuth deposits decreases while adopting a well-defined geometry as ammonium salt concentration increases. EDS analysis confirms that pure bismuth thin films were obtained and X-Ray diffraction indicates that the bismuth growth follows a preferential orientation along the (012) reticular plane.