Dynamic behaviour of a diffusion layer around a cation-exchange membrane in an external electric field

In this study we present an experimental device for studying the dynamic behaviour of spatial potential profiles around a cation-exchange membrane (CEM). We have designed and constructed a microdevice with integrated CEM. An array of golden microelectrodes is integrated around the membrane. The experimental arrangement used is capable of capturing the measured signal in sub-millisecond time intervals. We have studied the behaviour of the system using a galvanostatic mode in the area of the over-limiting current. The influence of two parameters is presented: (i) the effect of hydrodynamic mixing, and (ii) the effect of current density. Our results show that with increasing electrolyte flow both the total potential drop over the membrane and the width of the diffusion boundary layer decrease. With higher current densities the overall potential drop increases and also the potential profile changes are faster. The changes of potential profiles are related to changes in the concentration distribution of ionic species around the membrane. This type of experiments can also be used for verifying the local changes of electrolyte concentration during the process, for estimating the thickness of diffusion boundary layer and for validating the predictions of mathematical models that describe the dynamic behaviour of the system around the membrane. (C) 2010 Elsevier B.V. All rights reserved.