Abstract: Mass transfer at a gas evolving electrode was estimated by using a redox system of indicator ions.It was found that the absolute values of the slopes of 1gδ/1gi are 0.287 for hydrogen and 0.583 for oxygen generation in Ni/KOHsystem.The bubble size and velocity of bubble rise were measured by means of laser diffraction method and LDA.The data were used to examine the models of the mass transfer at gas evolving electrode (Hydrodynamic model and penetration model).It is concluded that the mechanism of enhance mass transfer from gas-evolving effects is not single.

Key words: Gas evolving electrode, Model of mass transfer, Indicator ions