Motion reversals of rising electrogenerated hydrogen bubble*

The growth of hydrogen bubbles in water electrolysis is of high practical relevance due to the prominent role of hydrogen in the future energy system. The dynamics even of a single bubble is already multifaceted and was recently found to be associated with Marangoni convection[1, 2], bubble-microlayer interaction [3, 4], and electric forcing [4].

In this contribution, the dynamics of hydrogen bubbles was studied during water electrolysis at a horizontal Pt microelectrode in an acidic environment. A new phenomenon triggered by jumps of the cathodic potentials was observed. It consists of the ability of already detached hydrogen bubbles, expected to continue buoyant rise, to reverse the direction of motion, and to return to the electrode from relatively large distances. 

The phenomenon was systematically studied at different time-dependent cathodic potentials and electrolyte concentrations by using high-speed microscopic shadowgraphy, the Schlieren method, and electric current measurements.