Behavior of water electrolysis accompanying gas evolution has been observed both under a microgravity and under a normal gravity. The water electrolysis has been performed at constant potentials on a gold plane electrode during about 20-25s of the microgravity condition available from parabolic flights of an aircraft. For each parabola the potential has been kept constant in the range of 2.5-15V vs. Pt wire. The bubble size increased instantly with decreasing gravity. On the other hand, current densities in high potential regions (9-15V vs. Pt) have drastically decreased under microgravity after an induced period of a few seconds. The reduced current densities, however, have never reached zero and have shown a certain minimum value. From the current-potential relationship, it has been suggested that the process of the water electrolysis under the microgravity condition is controlled by the mass transfer of water to the electrode surface, though the process under the normal gravity condition is controlled by the electrode reaction.
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