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DIVISION S-2—SOIL CHEMISTRY

Electrochemical Water Splitting at Bipolar Interfaces of Ion Exchange Membranes and Soils

^a Dep. of Civil and Environmental Engineering, Tri-State Univ., 1 University Ave., Angola, IN 46703
^b Dep. of Civil Engineering, Northwestern Univ., 2145 Sheridan Road, Evanston, IL 60208

* Corresponding author (desharnaisb{at}tristate.edu)

Under the influence of a direct current, the dissociation rate of water in contact with bipolar ion exchange membranes (BPMs) is 10⁶ to 10⁷ times faster than in free solution. This phenomenon, termed accelerated water splitting, is well known in industry where BPMs are designed for electrosynthesis of acids and bases. In this work, it is hypothesized that (i) accelerated water splitting can also take place at the bipolar interface between ion exchange membranes (IEMs) and the ion exchange surfaces of soils, and (ii) electroosmosis plays a key role. If the IEM has an electrostatic charge opposite in sign to the predominant charge on the soil colloidal particles, the interface is, in effect, bipolar. If an external electric field is then applied, conditions can give rise to accelerated water splitting. Laboratory experiments performed on various mixtures of Ottawa sand, bentonite, talc, and anion exchange resin indicate that accelerated water splitting occurs when the free pore solution in the low permeable soil moves away from the bipolar interfaces due to electroosmosis, thus causing an unsaturated zone at these interfaces. Accelerated water splitting then initiates at these interfaces since there are not enough counterions in contact with the IEMs to maintain an ionic current. Very little cation exchange capacity (CEC), anion exchange capacity (AEC), or clay is needed for water splitting to occur at a bipolar IEM and soil interface.

Abbreviations: AEC, anion exchange capacity • AEM, anion exchange membrane • BPM, bipolar ion exchange membrane • CEC, cation exchange capacity • CEM, cation exchange membrane • IEM, ion exchange membrane