HYDROGEN EVOLUTION STUDIES IN NEUTRAL MEDIA

The hydrogen evolution reaction (HER) was studied on platinum in weakly basic solutions of ammonium, lithium, sodium, and potassium sulfate by means of steady-state E-log j curves. To separate cation and pH effects it was necessary to determine the local pH at the electrode surface as a function of the bulk pH and current density, particularly for the unbuffered alkali-metal sulfates. This was done by placing the sensing tip of a pH electrode against the test electrode. Kinetic data were then extracted for those conditions under which the local and bulk pH values were equivalent. Such data indicate that the kinetics are equivalent for lithium, sodium and potassium sulfate; therefore, hydrogen evolution probably occurs by direct reduction of water in these solutions. Hydrogen evolution in 1 M ammonium sulfate is more rapid than that in 1 M alkali-metal sulfates by about 30 times, consistent with the idea that ammonium ions as well as water undergo direct reduction. The effects of ammonium-ion concentration and pH are consistent with direct reduction of ammonium ions.