Effects of Magnetic Field on Hydrogen Bubble Detachment during Water Electrolysis

Water electrolysis is a promising option for hydrogen production from renewable resources. One main challenge in making water electrolysis economically competitive is to raise its efficiency by decreasing the cell voltage. In this respect, electrode coverage by gas bubbles is one of the key sources which creates undesired overpotential.

Better understanding of the fundamentals of bubble nucleation, growth, and detachment in detail might bring new ideas in such effective manipulating of bubbles and substantially accelerate a way toward advanced electrolysis. Despite extensive efforts in the past, important aspects of bubble dynamics, such as the interaction/coalescence of bubbles significantly affecting their evolution or different growth modes of the bubbles themselves, are not yet fully understood. To provide that necessary information on the bubble shape profile, including the contact angle, the contact line the bubble forms with the electrode [1], the Marangoni convection[2], we use a micro electrode to produce single hydrogen bubbles. Water electrolysis was carried out under potentiostatic conditions in a 1 M H2SO4 solution in a small electrochemical cell ([2], [3], [4]). The behavior of a single hydrogen bubble evolving on a microelectrode (100 µm in diameter) was analyzed by measurements of the current transient as well as by microscopic high speed imaging. Tracer particles were additionally added to the solution to measure the flow in the vicinity of the bubble.

The contribution will present experimental results of the hydrogen bubble release size and the bubble growing mechanism at two different magnetic field orientations and at different field intensities. As shown in Fig.1, the bubble departure size decreased with increase of the magnetic field intensity when the magnetic field was applied parallel to the electrode surface. However, an increase of the departure size was observed when the field was applied perpendicular to the electrode surface. The effects were further explained by the MHD convection around the bubble. A comparison of the flow field by measurements and numerical simulation will be presented.