On the Dynamics of Hydrogen Bubbles at Pt Microelectrodes*

The growth of single hydrogen bubbles at Pt microelectrodes is studied during water electrolysis performed in an acidic electrolyte over a wide range of concentrations and cathodic potentials. New bubble growth regimes have been identified and summarized in the regime map. The regimes differ in terms of whether the bubble evolution proceeds with a monotonic or oscillatory variation of the electric current and if and how a carpet of microbubbles underneath the bubble evolves. Key features such as the growth law of the bubble radius, the dynamics of the microbubble carpet, the onset time of the oscillations, and the oscillation frequencies have been characterized as a function of the concentration and electric potential. Based on the analysis of the forces involved including electric and hydrodynamic (induced by Marangoni convection) forces, a sound hypothesis is formulated regarding the mechanism of the bubble oscillations and the evolution of a micro-bubble carpet.