Thermodynamic and kinetic behavior of hydrogen electrode in a solution of 0.5 M KClO4 in dimethyl sulphoxide

The hydrogen electrode on an interface platinum/dimethyl sulphoxide + 0.5 M KClO4 solution was examined from both the thermodynamic and kinetic aspect, using HCl as a proton source. The equilibrium potential was shown to obey a Nernstian dependence on concentration. The voltammograms recorded using a rotating platinum disc electrode evidenced that the cathodic evolution of hydrogen proceeds under mixed, activation diffusion control. The diffusion coefficient of the proton was determined to amount to 4.5×10-6 cm2 s-1. In the region of activation control, a Tafel slope of about 0.110 V dec-1 was estimated, which indicates that the Volmer reaction is the rate determining step.