The effect of electrolytically evolved gas bubbles on the thickness of the diffusion layer

Behaviour of a tall vertical gas-evolving cell. Part I: Distribution of void fraction and of ohmic resistance

“…The natural rise velocity of a single electrolysis bubble is in the order of 0.002 m s l [13]. Consequently, the effect of bubble slip at v~,0 = 0.56ms -I can be neglected.…”

“…The factors as and bs depend on vL0. Assuming the current distribution over the cathode is the same as that over the anode, the volumetric rate of the gas flow at a height h in the cell is given by f~ Vmiw e dh Qg,h -(n a q_ nc)F (13) where V m is the volume of 1 tool gas saturated with water vapour, na is the number of electrons involved in the anodic reaction, and nr is the number of electrons involved in the cathodic reaction.…”

Micro-scale mass-transfer variations during electrodeposition

“…Therefore, the bubble frequency must be measured independently by photographic or acoustic means. Janssen and Hoogland [158,159], for example, report that bubble volumes increase at current densities above 30 mA/cm 2 because of coalescence, lt should also be noted that neither the bubble size nor the speed of its ascent enter into the time-averaged current, since it is assumed that the replenishment of the reactant at the surface is complete and instantaneous.…”

“…Rising hydrogen bubbles generated in an acid solution are usually 60-80 um in diameter, while rising oxygen bubbles in the same low pH solution are generally smaller, approximately 40 um in size [ 127,138,158]. There is a dependence of size on the applied current, but it is not a reproducible one.…”

“…Janssen and Hoogland [158] observed that the speed with which bubbles rise past a vertical electrode does not stay constant with increasing height. Rather, there is an acceleration caused by convective currents.…”