Hydrogen absorption and desorption reaction on the platinum electrode

The processes of adsorption and evolution of hydrogen as well as its absorp tion onto the surface of platinum in both acidic and alkaline media have be en studied by the method of electrochemical impedance spectroscopy. In acid ic solutions the Nyquist plots consist of two overlapping semi-circles of v ariable diameters depending on the extent of the cathodic dc-potential offs et. The semicircle at the high frequency side of the spectrum enlarges upon increasing the cathodic shift and is associated to the surface H-upd, whil e the size of the semicircle at the low frequency end decreases in line wit h the behavior of the charge transfer resistance due to the evolution of hy drogen through surface H-opd. Equivalent circuits in perfect agreement with the experimental finding have been proposed and the values of the circuit elements and their correspondence with the electrochemistry of the processe s discussed. In alkaline solutions only one semicircle with its diameter de creasing upon the cathodic shift has been observed which is exclusively due to the process of evolution of hydrogen through H-opd.