Interlocking Bipolar Membranes for Efficient Electrochemical Separations

A bipolar membrane (BPM) is a special type of ion-exchange membrane in which an anion-exchange layer (AEL) and a cation-exchange layer (CEL) are combined. Water molecules can be easily dissociated at the interface of the BPM by the strong electric field generated when a reverse bias voltage is applied through the membrane. The generated proton and hydroxide ions move out through the CEL and AEL, respectively, to produce acid and base solutions. Meanwhile, under a forward bias condition, protons and hydroxide ions move to the bipolar interface and neutralized again. Neutralization energy is generated according to the concentration of proton and hydroxide ions which move through the BPM and can be expressed as a junction potential (JP) value. When a BPM having an ideal JP is applied to an electro-membrane process, high separation and energy efficiencies can be obtained. In addition, the BPMs should have a highly adhesive bipolar junction for the long-term operation of electro-membrane processes. In this work, a novel BPM with an ideal JP and a highly adhesive bipolar junction property was developed and applied to several electrochemical separation processes such as acid-base flow battery and direct seawater electrolysis. The specially designed BPM was fabricated with poly(phenylene oxide) (PPO) based ionomers. In addition, an iron-based catalyst and a reinforcing material were introduced for excellent water-splitting performance and interfacial durability between the two ion-exchange layers, respectively. The prepared BPM not only had excellent interfacial adhesiveness and mechanical properties but also exhibited high water-splitting efficiency of 98% or more. The electrochemical separation processes employing the prepared BPM exhibited excellent performances comparable with those of commercial BPMs. This work was supported by the National Research Foundation of Korea (NRF) grants funded by the Korean government (MEST) (NRF-2022M3C1A3081178 & NRF-2022M3H4A4097521).<br/> &lt;div id="__endic_crx__"&gt;&lt;div class="css-diqpy0"&gt; &lt;/div&gt;&lt;/div&gt;