Double Current Maxima Formed under Linear Potential Sweep Conditions in Acetic Acid Solutions at pH < 2.5

Resumo

The kinetics of hydrogen evolution on a copper electrode in acetic acid solutions is studied by the method of linear potential sweep. At рН < 2.5, double current peaks are observed with the height directly proportional to both √v (v is the potential sweep rate) and the total concentration of proton donors and acceptors. Upon the transition from the copper electrode to the platinum electrode, the overpotential of this process considerably decreases, but the shape of current peaks remains unchanged. The analysis of kinetics of acetic acid dissociation points to the high degree of lability of this system, which allows the relationship between the surface concentrations of its components to be expressed through the corresponding equilibrium constants. At certain potentials, significant changes in the surface pH are observed, which favor the appearance of an additional current peak in the cathodic chronovoltammogram. The Tafel plots normalized with respect to the surface concentration of hydrogen ions allow the following values of kinetic parameters to be obtained: i0 ~ 0.3 nA/cm² and α_c = 0.75. Chronovoltamograms simulated with the use of these values demonstrate double maximums which adequately agree with experimental data.