The electrochemical oxidation of white phosphorus at a three-phase junction

The oxidation of white phosphorus has been studied with graphite rods of varying diameters, which were partially embedded in solid white phosphorus placed on the bottom of a cell filled with aqueous electrolyte solution. During the first scan in linear sweep voltammetry, the current measured at various potentials is directly proportional to the length of the three-phase junction (tpj) line phosphorus|graphite|electrolyte solution. The currents are orders-ofmagnitude larger than predicted for a reaction that is strictly confined to a tpj line of atomic size and length of 4¯16 mm as used in the experiments. A model is presented which explains the reaction layer as built up of vitreous low-valent phosphorus oxides possessing electron hopping capabilities and ionic conductivity. It is assumed that the reaction starts at the tpj line, however, quickly converts to a reaction where electrons are transferred across an expanding face graphite|phosphorus oxides and where ions are transferred across an expanding face phosphorus oxides|electrolyte solution.