pH measurement in the vicinity of a cathode evolving hydrogen gas using an antimony microelectrode

An antimony microelectrode was prepared by quenching a molten Sb-Sb2O3 mixture (2% Sb2O3). The local pH in the vicinity of a cathode evolving hydrogen gas was directly measured using the microelectrode. The local pH during electrolysis of KCl-glycine aqueous solutions was increased by proton consumption; however, the increment decreased with increasing concentrations of glycine, a buffering agent. The diffusion-limiting current density of hydrogen evolution involving proton reduction was controlled by the concentrations of the proton-donating species: protonated-glycine (+HNCH2COOH)-N-3 and H3O+ ions. A plot of the current density against the sum of the concentrations gives a single straight line passing through the origin. The phenomena are discussed in terms of electrodeposition processes of base metals.