Single bubble growth during water electrolysis under microgravity

Single bubble evolution on a micro-electrode (Pt, phi = 0.2 mm) was observed in 0.36 M KOH solution under terrestrial (1-G) and microgravity (mu-G) environments. The bubble size during galvanostatic electrolysis (j = -2.6 x 10(3) A m(-2)) was measured by CCD images, which allowed us to calculate the gas evolution efficiency, f(G), by comparison with the consumed charge. The efficiency under mu-G increased until 1 s after starting electrolysis and then reached constant value (f(G) = 0.85), while, under 1-G. it showed a lower value and remarkably decreased 2 s after the beginning of the measurement. Such differences between mu-G and 1-G were explained by the mass transfer rate of the dissolved gas. Bubble-induced microconvection dominated the mass transfer under mu-G without any buoyancy force, on the other hand, the single-phase free convection (microscopic natural convection) influenced the bubble growth under 1-G. (C) 2009 Elsevier B.V. All rights reserved.