EFFECT OF THE NATURE OF THE ELECTROLYTE AND THE NATURE OF THE INTERFACE ON THE HYDROGEN EVOLUTION POTENTIAL: EXPERIMENTS FOR CHEMISTRY STUDENTS

This work presents an experiment done for chemistry students about the effect of the nature of the electrolyte and the nature of the interface on the hydrogen evolution reaction by electrolysis. Two techniques are suggested: method A - two identical copper electrodes in a direct current circuit and method B - three different electrodes in a dc potentiostatic circuit, with copper electrode (working), platinum electrode (counter) and silver-silver chloride-KCl sat electrode (reference). The hydrogen evolution was observed using the A technique by increasing potentials between the two electrodes and the visual observation of the gas production at the cathode. The results showed "semi-quantitative" effect of the pH on the hydrogen evolution. It was observed a larger potential difference in alkaline medium than in acid medium. The results obtained with the B technique from polarization curves showed quantitatively the thermodynamic effect of the pH in addition to the least catalytic effect of copper presented in alkaline medium when compared to copper in acid medium for hydrogen evolution. The technique A can be used in technical courses, high school and general chemistry class for under graduate students. The technique B is appropriate for under graduate electrochemistry class and graduate students.