Strong and Long-Lived Free-Radical Oxidizer Based on Silver(II). Mechanism of Ag(I) Electrooxidation in Concentrated H2SO4

Electrooxidation of silver(I) was studied in concentrated sulfuric acid and oleums at fluorine-doped tin oxide electrode. Electrochemical processes taking place at the electrode/solution interface have been investigated by using classical transient methods. We report a catalytic reaction pathway, in which one-electron transfer leading to solvated Ag(II) species is followed by a homogeneous chemical step with regeneration of depolarizer. By means of digital simulations this mechanism and the half-life of the Ag(II) complex was determined, tau(1/2) = 10 s. Activation energies of the electrode process and chemical reaction were found to be E-a,E-E = 52 +/- 5 kJ.mol(-1) and E-a,E-C = 60 +/- 5 kJ.mol(-1), respectively. The chemical step likely corresponds to a free-radical oxidation of HSO4- anions by Ag(II) radical species. Highly oxidative abilities of long-lived Ag(II) can be used for mediated electrochemical oxidation or electrochemical combustion.