Nanobipolar junction interfaces for ion-exchange membrane and resin materials for electrochemical systems

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1703307 ArgesWith increasing integration of renewable energy sources that provide emission-free electrical power, electrochemical technologies may soon extend beyond electric automobiles to also impact water treatment and chemical production. A familiar example of an electrochemical cell is the battery, in which electrons are released from a chemical species that has stored electrochemical energy. The electrons travel via a controlled pathway to complete the electrical circuit and provide electricity. As the electrons are negatively charged, positively charged ions (for example, battery acid) must simultaneously converse a physical barrier to maintain charge neutrality. A solid-state polymer electrolyte separator provides these controlled and separate pathways that simultaneously channel electrons and ions. In an environment that is often quite corrosive and reactive, this separator must be chemically, electrochemically, thermally, and mechanically stable. To minimize unwanted energy and power losses, resistances to the transfer of electrons must also be minimized, which can be accomplished via molecular-level design of the separator. This project focuses on molecular design and optimization of a relatively unexplored class of polymer electrolyte separators, called bipolar membranes. A bipolar membrane incorporates a junction of positively and negatively charged molecules at a shared interface for water splitting electrochemical reactions. Electrochemical water splitting enables conversion of transient renewable power to chemical energy for long term storage. This project will engineer the bipolar junction on a molecular-level scale to minimize energy losses, with potential impact to a number of electrochemical technologies.This project aims to overcome some of the current limitations of bipolar membranes by correlating interfacial area in the bipolar junction to water-splitting kinetics and mass transport related resistances of water and ion species. Uncovering this correlation is anticipated to yield lower resistant bipolar membranes that translate to lower energy footprint electrochemical reactor-separator processes. The central hypothesis of the project posits that an inverse, commensurate relationship exists between cell overpotential for water dissociation and bipolar junction interfacial area. Testing the central hypothesis will be accomplished by fabricating precisely defined bipolar junction interfaces via two approaches: i.) constructing 2D bipolar junctions on substrate surfaces through block copolymer lithography and ii.) nanopatterning bulk membrane surfaces through nanostructured molds afforded from block copolymer templates. The expected outcomes will reveal how the salient structural features of bipolar junction interfaces govern electrochemical cell performance when splitting water. Finally, the project will contribute to the training of a future STEM workforce prepared to address future challenges in the water-energy nexus, and it will spark 8th and 9th grade students' interest in math with outreach activities that illustrate the utility of algebra principles to materials design.