Modelling the chronopotentiometric response of constant current hydrogen evolution from dilute solutions of strong acids

Cathodic hydrogen generation from unstirred dilute acids (2 < p H < 7) often results in the vicinity of the electrode turning alkaline. Potential transients recorded at constant current exhibit a sharp step at the moment of surface neutralisation, and the stepped chronopotentiograms convey important information with regard to the rate of both the electrode reaction and of mass transport. Here we present a robust model that, although it contains only three variable parameters, can fit chronopotentiometric measurements. The reaction rate and charge transfer coefficients obtained from the fitting can be combined into a p H dependent exchange current density of HER that can be used for benchmarking the catalytic activity of different electrode materials, while the obtained diffusion coefficient can be applied in simple formulae to estimate the characteristic time of surface neutralisation and the rate of propagation of the neutrality front. • Chronopotentiograms (CPs) of HER show characteristic steps in mildly acidic solutions. • A model is developed to determine the main charge transfer parameters. • Using these, the electrocatalytic activity of electrodes is benchmarked.