Electrosorption impedance on Pt(111) in sulphuric media and nature of the "unusual" state

Impedance measurements, up to 1 MHz, not only in sulphuric acid but also with supporting electrolytes for H+ or for anions, confirmed that the usual peaks on Pt(111) are related to a fast hydrogen electrosorption, and that the "unusual" state is due to sulphate anion electrosorption on the whole pH range, or to hydrogenosulphate at low pH and to sulphate above pH 2.