The anodic oxidation and open circuit decomposition of H2O2 on UO2+x, surfaces have been investigated voltammetrically and using linear polarization resistance measurements over the pH range 9.5 to 12.6. At the lower pH values both the anodic oxidation and decomposition reactions are almost completely blocked by a thin surface layer of U-VI oxide. At higher pH this layer becomes more soluble and anodic oxidation occurs on the sublayer of (U1-2xU2xO2+x)-U-IV-O-V, but is partially controlled by transport through a permeable; chemically dissolving U-VI oxide/hydroxide layer. At positive electrode potentials (0.3 V vs. saturated calomel electrode), approximately 70% of the anodic current is consumed by H2O2 oxidation the remaining 30% going to produce (UO2)-O-VI(OH)(x)((2-x)+). At higher pH values, H2O2 decomposition occurs on an unblocked (U1-2xU2xO2+x)-U-IV-O-V surface and the pH dependence of the reaction suggests HO2- is the electroactive form of peroxide (C) 2014 Elsevier Ltd. All rights reserved.