Cathodic hydrogen evolution from aqueous solutions of acetic acid

In continuation of the work on establishing hydrogen donors in the hydrogen evolution reaction from different acid molecules, cathodic evolution of hydrogen on silver is investigated from solutions of monobasic acetic acid with the aim to establish the origin of reduced hydrogen. Solutions of 0.2 M acetic acid with 0.2 M perchloric acid, neutralized to different pH values by NaOH, are used. The earlier established criterion is used for discerning between two possible hydrogen evolution mechanisms: (1) from dissociated hydrogen ions and (2) from undissociated hydrogen atoms in the molecule. At medium pH values, the undissociated acid molecules participate as hydrogen donors. Rate constants for reactions 1 and 2, evaluated at a potential of -800 mV (SCE), at which the entire pH range can be scanned, are 2.9 x 10(-6) and 1.9 x 10(-8).