Electrochemical studies at low temperatures, XII. Barrierless mechanism of hydrogen evolution on solid Ga electrodes

The temperature dependence of hydrogen evolution between 273 and 233 K was studied on gallium electrodes in solutions of 4.2 m HClO(4) acid in the range of over potentials eta: -0,50 - -0,75 V. We have found that in the case of Ga metal the eta - lg j curves obtained can be divided into two sections: in the eta: -0,50 - -0,65 V interval the slopes of the curves are smaller (0.06 V), while at eta < -0.65 V they are greater (0.10 V). In the range between -0,50 - -0,65 V the values of the charge transfer coefficient beta are 0,77 - 0,86, suggesting that here the barrierless mechanism of the hydrogen evolution reaction takes place. In this interval of overpotential above freezing point of the solution, between 273 and 243 K the value of the activation energy for Ga electrodes equals 44 kJ mol(-1). A comparison of the data obtained on Cu and Ag electrodes [1] and measured on Ga electrode shows that a decrease of the activation energy causes an increase of the M - H(a) bond enthalpy. These latter experimental results suggest that the r. d. s. is the electron transfer. Below the freezing point of the solution (between 238-228 K) at low values of eta (-0,50 - -0,65 V) the eta - 1g j curves with beta approximate to 0.77 - 0,86, show that the barrierless process of hydrogen evolution is not affected by the state of the electrolyte.