Studying the contact electric resistance of platinum in aqueous solutions

The contact electric resistance (CER) R of platinum is studied depending on the potential E in the pH range from 0 to 14. In all the solutions examined, the R-E curves are bell-shaped with the maximum around 0.4 to 0.5 V (EHE). This shape is relatively insensitive to the concentration and nature of the electrolyte and changes only upon adding strongly adsorbing anions to the solution or upon replacing water as a solvent with dimethyl sulfoxide. In alkaline solutions, the CER of platinum increases with an increase in the concentration of hydroxide ions, which is explained by the sensitivity of the CER to the adsorption of hydroxide ions on platinum. Their adsorption is shown to begin in the hydrogen range of potential. A sharp decrease in the CER of platinum in acidic, neutral, and alkaline solutions is observed at E greater than or equal to 0.4 V (EHE) and accounted for by the beginning of the noticeable charge transfer from the adsorbed hydroxide ions to the metal. The isotherms of the adsorption of hydroxide ions on platinum in alkaline solutions at E less than or equal to 0.4 V (EHE) are considered.