Reactions of Bromide and Iodide Ions with Silver Oxide Films on Ag Substrates

Abstract

Conversion of an Ag2O film on a Ag substrate to AgX in a halide solution occurs via three competing reaction pathways: (1) chemisorption of a halide ion, X−(aq) onto Ag2O followed by reaction to form AgX, (2) electrochemical oxidation of the Ag in the metal substrate to form AgX coupled with reduction of Ag2O to form Ag, and (3) dissolution of Ag2O followed by reaction of Ag+(aq) with X−(aq) to form AgX(aq) and deposition of the AgX. In this study, Ag2O films of different thicknesses were grown potentiostatically on Ag electrodes in 0.01 M NaOH solutions. Reactions of the Ag2O films with halide ions were initiated by transferring the electrodes into 0.01 M NaOH solutions containing I− or Br−. The reactions were followed by monitoring the open circuit potential (EOC) on the Ag electrode. The open circuit potential shows a sharp change upon completion of the reaction and this allows an easy determination of the reaction time. The reaction time as a function of halide concentration, the Ag2O film thickness, and the electrode rotation rate was measured to determine reaction kinetics parameters. Additionally, potentiodynamic and galvanostatic reduction of the AgX film was measured. The data from these different measurements were used to elucidate the contributions of the three pathways to the overall conversion process.