The electrochemical behaviour of trivalent chromium (Cr3+) in 1-butyl-3-methylimidazolium tetrafluoroborate [BMIm][BF4] ionic liquid solutions was studied by cyclic voltammetry and chronoamperometry. The reduction of Cr3+ occurs in two steps, Cr3+ to Cr2+ and Cr2+ to Cr-0 respectively. The first step is quasi-reversible with a diffusion coefficient of CO in solution of 3.13 x 10(-8) cm(2) s(-1) at 303 K and 25.8 x 10(-8) cm(2) s 358 K, estimated from cyclic voltammetry data. Black chromium films were electrodeposited on copper, stainless steel and carbon steel substrates at a constant potential of 1.5 V vs Pt quasi-reference electrode. The films consist of aggregates of nanosized particles. The coatings in the as-deposited condition present an amorphous structure but after annealing for 4 h, a nanocrystalline Cr2O3 phase is formed, with an average crystallite size of 17 nm. (C) 2011 Elsevier Ltd. All rights reserved.