Electrochemical mechanism of trivalent chromium reduction in 1-butyl-3-methylimidazolium bromide ionic liquid

• [BMIM]Br shows a good electrochemical stability and diffusion coefficient of Cr3+ is larger in it.
• Reduction of Cr3+ occurs by a two-step process, and the process is an irreversible.
• Two-step process is identified by chronopotentiometry.
• Cr coating with ball-like crystal structure can be prepared from [BMIM]Br.
• Chromium depositing takes place by an instantaneous nucleation growth mechanism.

The electrodeposition and electrocrystallization behaviour of chromium reduction in 1-butyl-3-methylimidazolium bromide ([BMIM]Br) ionic liquid on a glassy carbon (GC) electrode is investigated. These results from cyclic voltammetry and linear sweep voltammetry show that the reduction of trivalent chromium (Cr3+) occurs by a two-step process, Cr3+ to Cr2+ and Cr2+ to Cr0, respectively, the first step is an irreversible process with a diffusion coefficient of Cr3+ in solution of 2.3 × 10−6 cm2 s−1 at 358 K, and the two-step reduction reaction has been identified by chronopotentiometry. The electrodeposits are characterized by SEM, EDS and XRD. XRD pattern of the electrodeposited layer reveals the characteristic peak of crystal Cr. Chronoamperometry results provide direct evidence that chromium electrodeposition in [BMIM]Br takes place through an instantaneous nucleation and diffusion-controlled three-dimensional growth mechanism.