X-ray photoelectron spectroscopy (XPS) is used as a probe of the interaction between rhodium acetate ([Rh-2(OAc)(4)]) and ionic liquids. Due to the impact of the anion of ionic liquids on the electronic environment of the rhodium centre, the measured Rh 3d binding energies of [Rh-2(OAc)(4)] dissolved in a series of ionic liquids were found to decrease along with the increasing of the basicity of anions. The reduction of Rh(II) to Rh(0) in 1-octyl-3methylimidazolium acetate ([C(8)C(1)Im][OAc]) under UHV condition was monitored by XPS. The intensity of the new formed metallic Rh(0) peak was found increased along with time. The surface enrichment of the new formed Rh(0) species in the system was also concluded. (C) 2016 Elsevier B.V. All rights reserved.