Chemical and textural changes in a commercial Nafion‐112 membrane as a result of its doping with the cation of the room temperature ionic liquid (RTIL) tricaprylmethylammonium chloride (Aliquat+) are analysed by X‐ray photoelectron spectroscopy (XPS), contact angle and atomic force microscopy (AFM). The XPS results show changes in the membrane surface as a result of partial coverage by the RTIL‐cation, taking into account the increase in the doped sample surface of the atomic concentration percentage of nitrogen (Aliquat+ characteristic element) and the reduction in the percentage of fluorine (Nafion characteristic element), as well as the reorientation of the sulfonic groups. Nafion surface modification also causes a decrease in the hydrophobic character according to water contact angle values. Moreover, the AFM measurements demonstrate an increase in the surface roughness of the doped membrane, and the presence of clusters of different shapes and sizes, being consistent with a rearrangement of the Nafion surface, in agreement with XPS results. Copyright © 2016 John Wiley & Sons, Ltd.