The effect of Triton X-100 (nonionic surfactant) and cetyltrimethylammonium bromide (CTAB), cationic surfactant, on the mass transfer coefficient of the cathodic reduction of ferricyanide ions and anodic oxidation of ferrocyanide ions at hydrogen- and oxygen-evolving electrodes, respectively, was studied. It was found that the limiting current decreases by amounts ranging from 26.67 to 54.67% for Triton X-100 and from 20 to 46.0% for CTAB in the case of cathodic reduction of ferricyanide ions under natural convection at H-2-evolving electrodes and from 23.81 to 51.43% for Triton X-100 and from 18.10 to 40.95% for CTAB in the case of anodic oxidation of ferrocyanide ions under natural convection at O-2-evolving electrodes, depending on the concentration of surfactant. Also the effects of Triton X-100 and CTAB on the gas hold-up and cell voltage were studied. The presence of surfactant in electrolytes was found to decrease the mass transfer coefficient by an amount ranging from 5.37 to 95.9%, depending on the operating conditions. Gas hold-up, cell voltage, and power consumption were found to increase in the presence of surfactant. (C) 2004 Elsevier Inc. All rights reserved.