PNNL

Abstract

Open circuit potentials were measured for acetonitrile solutions of a variety of acids and their conjugate bases under 1 atm H2. Acids examined include triethylammonium, dimethylformamidium, 2,6-dichloroanilinium, 4-cyanoanilinium, 4-bromoanilinium, and 4-anisidinium salts. These potentials, together with the pKa values of the acids, establish the value of the standard hydrogen electrode (SHE) potential in acetonitrile as -0.028(4) V vs the ferrocenium/ferrocene couple. Dimethylformamidium is shown to form homoconjugates and other aggregates with dimethylformamide; open circuit potentials are used to quantify the extent of these reactions. Overpotentials for electrocatalytic hydrogen production and oxidation were determined from open circuit potentials and voltammograms of acidic or basic catalyst solutions under H2. This method requires neither pKa values, homoconjugation constants, nor an estimate for the SHE potential and thus allows direct comparison of catalytic systems in different media.