A multiscale-pore ion exchange membrane for better energy efficiency

Abstract

Ion exchange membranes (IEMs) have been adopted in various environmental, chemical, and energy applications. However, the formation of ion-depletion regions, caused by concentration polarization near IEMs, often leads to significant energy and efficiency loss. While much research has been devoted to solving this challenge, complete removal of ion-depletion regions is still difficult, especially when the membrane systems are operating under near- or over-limiting conditions. This paper proposes a novel multiscale-pore (MP) IEM to reduce the effect of the ion-depletion region, by allowing a fluid flow through the MP-IEM, thereby limiting the size (and the resulting resistance) of the ion-depletion region. The electrical resistance and energy consumption in MP and conventional IEM-embedded electrochemical systems were investigated, and their performance during water desalination processes were compared. The current–voltage response suggests a secondary ohmic regime attributed to an internal flow rate through the MP-IEM. Moreover, the electrochemical desalination of seawater with MP-IEMs demonstrated up to 75% reduction of energy consumption, compared with conventional IEMs under comparable operating conditions.