Potentiostatic electrolysis of a mixed aqueous solution of Bu(4)NBr and MnSo(4) at +1.0 V (vs. Ag/AgCl) on Pt electrode led to the oxidation of Br(-) and Mn(2+) ions. X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and X-ray diffraction (XRD) revealed that this anodic process was followed by the deposition of insulating crystals of bromide salt of Bu(4)N(+) and the subsequent formation of layered manganese oxide in the interstitial spaces of the bromide grains already grown. Dissolution of the bromide crystals in water left a well-dispersed porous texture composed of manganese oxide nanosheets. The resulting MnO(x)-modified electrode exhibited a larger catalytic current for the reduction of oxygen in alkaline solution, compared to the bare Pt electrode. (C) 2008 Elsevier Ltd. All rights reserved.