Ohmic Resistance Measurement of Bubble Froth Layer in Water Electrolysis under Microgravity

Abstract

Galvanostatic water electrolysis was conducted in 2 wt % KOH and 0.1 N H 2 SO 4 solutions under microgravity. The corresponding terrestrial experiments employed two kinds of electrode configurations: a vertical cathode and downward-facing horizontal cathode-over-anode ͑C/A͒ arrangement. The latter configuration was designed to simulate the microgravity ͑-G͒ condition. The ohmic resistance of the gas bubble dispersion zone near Pt electrodes was measured by the current interrupter method and compared for these three different cases. The transient variation of resistance for C/A configuration behaved similarly to that under -G in H 2 SO 4 , but the resistance varied more slowly in KOH. When water electrolysis was conducted with a vertical plane cathode under 1-G, the resistance reached an essentially constant value within a few 100 ms in KOH, whereas the resistance increased linearly for a few seconds, followed by a zig-zag variation in H 2 SO 4 . Water electrolysis under -G resulted in stable froth layer formation, and the accompanying ohmic resistance increased in linear proportion to the froth layer thickness. The contributions of electrode surface coverage by bubbles and electrolyte-phase bubble void fraction to the ohmic drop were also assessed. These parameters were compared with corresponding values in terrestrial experiments analyzed by Balzer and Vogt.

Hydrogen production by alkaline water electrolysis

“…Detachment of the bubbles also depends on the electrode wettability, i.e., on the electrolyte replacement at the electrode/electrolyte interface. 96,97 Appropriate coatings can be applied on the electrode surface to make it more hydrophilic, thereby reducing the surface coverage by gas bubbles. Another approach is based on the addition of surfactants to the electrolyte solution to reduce its surface tension and facilitate detachment of bubbles from the electrodes.…”

“…In summary, the bubble effect is a problem that has always to be dealt with, by modifying the electrode surface, reducing the electrolyte surface tension, or using mechanical fluid circulation to force the gas bubbles to leave the cell. Much work has been devoted to the bubble behavior in electrolysis systems, 96,[98][99][100][101] but further studies are still required to minimize its negative effects.…”

“…The dissolved gas bubbles and the gas interfaces between electrodes and electrolyte generate large resistances to water electrolysis. The bubble phenomena have been studied intensively, 96,201,202 but no mechanisms or models have yet been applied to alkaline water electrolysis. The contributions of the electrode surface coverage by gas bubbles and the electrolyte--phase bubble void fraction to the Ohmic drop have been discussed.…”

Status and Prospects of Alkaline Electrolysis

“…Bubble behavior has been intensively studied [98][99][100] in the sense of electrochemistry, but no mechanisms or models have been applied to alkaline water electrolysis. The microgravity condition under which the buoyancy effect is eliminated has been used to study the bubble behavior.…”

PEMFC Performance in a Magnetic Field

“…Most experiments have been performed in the underground laboratory of the Kyoto University during the winter season. The experiment was thus carried out at the relatively low temperature of 281 K. Nevertheless, this is convenient in some aspects, because our research group [18][19][20] targets at the effective utilisation inside a space craft where the fuel cell may be sometimes operated at relatively low temperatures. The magnetic field is considered as one promising tool to improve the mass transfer and to achieve a high output performance under such special conditions.…”