When a charge selective surface consumes/transports only cations or anions in the electrolyte, such biased ion rejection initiates hydrodynamic instability, resulting in vortical fluid motions on the surface. In this thesis, we describe the first laboratory observation of three-dimensional electroconvection on an ion-exchange membrane. Combining experiment and scaling analysis, we successfully categorized three distinct patterns of 3D electroconvection as polygonal, transverse, or longitudinal rolls.