Platinum nanoparticles are used as catalysts in most proton-exchange-membrane fuel-cells (PEMFC). A major issue with their use is the problem of catalyst poisoning by the adsorption of anions. In hydrogen-bromine fuel cells and electrolyzers, bromides and bromine species migrate across the membrane and poison the hydrogen-electrode catalyst, thereby reducing the electrode activity. The adsorption of bromide ions is thus a critical factor which must be studied. in this work, the adsorption of bromide ions and the hydrogen redox reactions were studied, for the first time, on XC72-supported platinum nanoparticles in concentrated HBr solutions with the use of rotating-disk-electrode and cyclic-voltammetry techniques. It was found that in 3M HBr, the charge related to Pt-H desorption decreased by 30% relative to the charge obtained in 0.5 M sulfuric acid, and only a small part of the adsorbed bromide is released at zero volts: In addition, the HOR/HER exchange-current density decreases as a result of bromide adsorption. (C) 2011 Elsevier B.V. All rights reserved.