Complete Suppression of Dispersed Inorganic Precipitates in Reverse Electrodialysis via Seawater Acidification

Abstract

A large-scale reverse electrodialysis (RED) system consists of several hundred cell pairs, resulting in a stack voltage of tens of volts at the ends of the electrodes. Under this high voltage condition, water reduction/oxidation inevitably occurs despite the presence of redox couples, which means that a continuous supply of redox couples is required for long-term operation due to their instability under sudden changes in pH around the electrodes. On the other hand, water electrolysis can be used as an electrode reaction in natural seawater, without chemical reagents. However, inorganic precipitation by hydroxide ions produced in the water reduction reaction is a persistent problem that hampers cathode operation in seawater, because the deposits decrease the electrochemically active surface area of the cathode and hinder ionic flow across the ion exchange membranes. It has recently been demonstrated that seawater acidifies to pH 3 via a cooperative effect between proton flux from a bipolar membrane and inorganic precipitation at the cathode interface. In this study, seawater acidification was applied to the RED system to completely suppress dispersed inorganic deposits, enabling the stable operation of large-scale RED stacks without clogging problems. This result opens the possibility of developing an environmentally friendly RED system that does not use any chemical reagents.

Multi-scale physics of bipolar membranes in electrochemical processes

“…103). Other strategies in improving BPM resilience towards inorganic precipitation include modifying the electrode porosity, introducing open areas not in direct contact with the electrode, and recovery procedures such as pulsing electric-field polarity and feed acidification [110][111][112][113] .…”

Ion sieving membrane for direct seawater anti-precipitation hydrogen evolution reaction electrode

“…14,15 Moreover, HER electrode precipitation also causes problems for other applications, such as electrochemical sewage treatment, sodium hypochlorite production from seawater, and metal seawater batteries. [16][17][18][19][20][21] Therefore, an ideal method to solve HER electrode precipitation is urgently needed for applications.…”

Ion Transport Behavior in Bipolar Membrane Electrodialysis: Role of Anions

“…The transport of ions through ion-exchange membranes is a critical factor in maximizing energy efficiency and productivity in the electro-membrane processes used in water treatment, clean production, and energy harvest processes, such as electrodialysis (ED), , Donnan dialysis, bipolar membrane electrodialysis (BMED), , reverse electrodialysis (RED), , and membrane capacitive deionization (MCDI) . These processing mechanisms involve ionic migration via a charged polymeric membrane (anion- and cation-exchange membranes and bipolar membranes).…”