Ionic Polymer-metal Composites (IPMCs) are soft actuators and sensors. They generally consist of a thin perfluorinated ionomer membrane, metal electrodes plated on both faces, and are neutralized with certain counter cations, balancing the charge of the anions covalently fixed to the membrane. Under a suddenly applied step function (1 to 3 V), the IPMC in alkali-metal cation forms exhibits a fast bending motion towards the anode, followed by a slow relaxation. For Nafion-based IPMCs, this slow relaxation is towards the cathode, whereas for Flemion-based IPMCs, the slow relaxation continues the initial fast motion towards the anode. IPMC samples in sulfonic forms having sodium as cations are prepared, their electromechanical properties are characterized, and their actuation responses to various electric stimuli are investigated. Results show that for Nafion-based IPMCs, initial motion towards the anode can be ultimately eliminated by applying a slowly increasing potential, due to very slow charge accumulation and extensive cation redistribution within a boundary layer near the cathode electrode.