Steady state voltammetry in the process of hydrogen evolution in buffer solutions

The process of hydrogen evolution occurring at a platinum microelectrode was studied in buffer solutions made by either mono- or polyprotic acids. Buffers formed either by mixing equal amounts of the weak acid and its conjugate base, or an excess of acid or base were considered. The results demonstrated that the steady state limiting current, Il, is related to the amount of both free proton and undissociated acid present in the mixture, even if the pH of the solution is constant or changes to a negligible extent. Linear trends, between the steady-state limiting current and the analytical concentration of the weak acid, CA, present in the mixture, was found in the buffers, while comparative measurements carried out in solutions containing the weak acids alone, showed that the plots are not linear. Theoretical relationships relating Il and CA directly were also derived, and they allowed to rationalise the fact that all the buffers formed from a given monoprotic acid display plots having a common slope, while the buffers obtained from a polyprotic acid may show plots with different slopes.