The voltammetric profile in sulfuric acid electrolytes of high coverage bismuth monolayers on Pt(lll) having a fractional coverage (theta) of 0.39 exhibits two pairs of peaks located positive and negative, respectively, of the redox peak associated with the 0.33 coverage Bi/Pt(111) adlayer. The Delta E-fwhm (full width at half-maximum) values for these peaks are 10 and 20 mV, respectively, suggesting that the redox events involve significant near-neighbor interactions and may correspond to phase transitions within the bismuth adlayer. The formal potentials of these redox peaks shift by 65 mV per pH unit, suggesting that two protons are involved in the two-electron redox reaction of the bismuth adatoms, This provides evidence that the two pairs of redox peaks could correspond to the abrupt formation of [Bi(OH)(2)](ad) and [BiO](ad) from Bi-ad. Upon continuous potential scanning in sulfuric acid electrolyte, these peaks decay while two new peaks grow in, with an isopotential point forming between the two anodic peaks. The new, latter peak corresponds to that found for the 0.33 coverage Bi/Pt(111) adlayer. The peaks that grow in upon potential scanning could arise from the interconversion of the hydroxide and oxide network to a stable, long-range hydrogen-bonded (bi)sulfate network upon bismuth oxidation. The peak associated with the 0.33 coverage Bi/Pt(111) adlayer could then be ascribed to the abrupt formation of this (bi)sulfate network upon bismuth oxidation. In perchloric acid electrolytes the two pairs of high coverage bismuth redox peaks are also present, but one increases monotonically while the other decreases upon potential scanning, without the appearance of any new peaks. The high coverage peaks are thus associated with the formation of a long-range hydroxide and oxide network upon bismuth oxidation. The presence of halide anions (Cl-, Br-, I-) dramatically affects the voltammetric profile of Bi/Pt(lll), Initially, chloride appears to form a complex with the bismuth adlayer. Upon potential scanning, the redox peak ascribed to the chloride complex decays while that associated with the stable bismuth adlayer reemerges, Bromide and iodide anions both cause the complete desorption of the bismuth adlayer, suggesting that they have significantly stronger bonding interactions to Pt(lll) than does bismuth.