Electrodialysis Pump Based on Enhanced Water Dissociation of Bipolar Membrane

Abstract

We describe a novel micropump mode–electrodialysis pump (EDP), which is based on the recombination of hydrogen and hydroxyl ions generated by enhanced water dissociation of bipolar membrane (BPM). The pump is in a sandwich-like configuration in which the central production channel is spatially isolated from two outer regenerant chambers by a BPM, respectively. Both BPMs are put at the same direction, in which the anion exchange membrane (AEM) side is facing the anode with respect to the cation exchange membrane (CEM) side facing the cathode. Pure water as the feed solution flows through the regenerant chambers at a conventional flow rate (e.g., 0.2 mL/min). Under the electric field, enhanced water dissociation at the junction layer of BPM will occur, generating hydroxyl and hydrogen ions. Their electrodialytic migration into the central channel will recombine water and its flow rate is correlated with the applied current. The pump shows near-ideal Faradaic efficiency and at least 0.8 μL/min can be achieved by controlling the current. The produced water is near neutral and obvious enrichment of trace impurity anions is observed in the production channel.

Recent Advances in Bipolar Membrane Design and Applications

“…A salt solution is passed between a CEM and an AEM, where under operation the Na ions and Cl ions electrodiffuse into separate compartments to combine with the hydroxide ions or protons generated by the BPMs, with water-splitting reactions occurring at the electrodes to complete the system. Dilute NaOH and HCl solutions are initially introduced into the product streams to reduce the cell resistance, with the NaOH and HCl concentration increasing during BPMED, Figure . ,, Here, the BPMs act as the acid/base source and electrode protective layer, ensuring the electrodes are operating under optimal solution conditions for water splitting while minimizing product crossover into the electrode compartments. , The salt solution can be continuously diluted via a closed-loop process until a desired level of desalination is achieved. ,, Complete desalination or production of commercially available concentrations of HCl and NaOH by BPMED alone is not possible due to the electroosmotic drag of water into the acid/base compartments by ion diffusion, where water acts as the ion solvation shell, as well as the high resistance that results from operation on a dilute salt solution. − …”