On mass transfer effect due to electrolytically evolved gas

Based on the Ibl penetration model mass transfer equations for gas-evolving electrodes were derived and compared to the effect of forced convection. Experimental studies were conducted in a rectangular flow channel with the working electrode facing downward. The variables were linear bubble velocity, linear electrolyte velocity, nature of the gas and electrode position. Up to bubble velocities (U_x) of 2 and 6 cm s^?1 for O₂ and H₂ gases respectively, the thickness of the Nernst diffusion layer (δ_av) was described well by the equation δ_av = Dd_eL/(U_x)_av]^1/3. Intermediate slopes between ? 1/3 and ? 1 were observed for O₂ bubble velocities between 2 and 6 cm s^?1. A theoretical derivation suggests that in the absence of bubble coalescence, the mass transfer effect due to laminar flow induced by electrolytically evolved gas exceeds that due to forced external laminar flow for all practical channel designs.