Positive Platinum Sols

Abstract

A DETAILED investigation on the adsorptive properties and the capacity of platinum electrodes, made by A. Frumkin and A. lygin¹, has led to the conclusion that there may exist, besides the negative platinum sol with oxides on the surface of the particles, which has been described by Pennycuick, two further varieties of platinum sols. One of them should be a negative sol, with its surface coated with a film of adsorbed hydrogen, the outer part of the double layer consisting of cations. The other should be a positive sol with a double layer, the outer part of which is formed by anions. According to the results obtained with platinum electrodes, it was expected that positive sols would be obtained by a careful oxidation of negative H₂-platinum sols. These positive sols must themselves be transformed by further oxidation into the usual negative sols. These conclusions were announced by A. Frumkin at the discussion on ” Colloidal Electrolytes” held by the Faraday Society in September 1934²; it remained uncertain, however, whether the stability of positive platinum sols, which is determined mainly by an electrical double layer, is such that it would be possible to prepare them.