Optimizing the molecular design of pyridinium anolytes for energy storage applications

Madison Shaffer and Dr. Thomas Guarr

Redox flow batteries (RFBs) offer a safe and environmentally friendly alternative for grid-scale energy storage applications.  The organic materials used in these batteries must meet certain criteria in order for the battery to work efficiently.  Specifically, the anolyte must have a low reduction potential, stable reduced state, and high solubility.  A well-known pyridinium salt, methyl viologen, is commonly used as an anolyte, and previous work in our lab has led to the discovery of new pyridinium salts that offer lower reduction potentials and greater stability.  However, the solubility of these systems is typically low, limiting the energy density of RFBs incorporating such materials.  It has recently been discovered that small changes in molecular structure can cause an increase in C-H – pi-interactions, which results in a dramatic increase in solubility (1).  This work emphasizes the optimization of the molecular design of pyridinum anolytes and the effects it has on overall solubility.

1  C–H···π interactions disrupt electrostatic interactions between non-aqueous electrolytes to increase solubility published in Nature Chemistry

Madison graduated from Alma College (another one!) this spring with a degree in Chemistry.  We are really excited that she has decided to stick around our lab for a while and continue to help us with some great research.  Thanks Madison!  I hope you enjoy it here.  We love having you.

Evaluating ionic liquid pyridinium compounds for non-aqueous redox flow batteries

Ed Zornow, Dennis Downing and Dr. Thomas Guarr

The energy capabilities of aqueous Redox Flow Batteries (RFBs) are limited by the use of water as a solvent which has a narrow potential window, resulting in relatively low energy density.  In addition, many redox-active compounds of interest are not highly soluble in aqueous electrolytes.  Using non-aqueous electrolytes in RFBs can circumvent these issues.  Ionic liquids are organic salts that are in the liquid state at room temperature and exhibit attractive electrolyte properties such as wide potential windows, and high conductivity.  Furthermore, by using a redox-active compound as the basis, solubility is maximized since there is no additional solvent or electrolyte salt.  Functionalizing pyridinium compounds with hydrocarbon or oligoether chains to form ionic liquid derivatives has the potential to provide effective and recyclable electron carriers for non-aqueous redox-flow batteries.  Several pyridinium compounds of various functionalizing groups with hydrocarbons were synthesized and characterized via NMR, mass spectrometry, and cyclic voltammetry.

Ed graduated in the spring with a Chemistry degree from Notre Dame.  He spent the summer synthesizing pyridinium compounds in our lab.  Ed is a great guy and we are waiting to hear what his future holds.

Synthesis of novel carbazole derivatives for electrochemical applications

Daniel Swanson, Dennis Downing, and Thomas Guarr

Carbazoles are of particular interest for electrochemical applications such as redox-flow batteries (RFBs) because of their ability to undergo reversible electrochemical oxidation at high potentials.  Polymerization of the carbazole radical cation decreases reversibility but can be subdued by blocking areas of high electron-spin density (1-,3-,6-, and 8-positions).  Functionalization with electron-withdrawing groups has been shown to cause an increase in oxidation potential.  Moreover, the addition of alkyl groups distorts the preferred planar geometry of the radical cation.  Using an intramolecular oxidative coupling route previously discovered in our lab, we synthesized several carbazole derivatives bearing electron withdrawing groups at the 3- and 6-positions and methyl groups at the 1- and 8-positions.  These carbazole derivatives were synthesized with the eventual goal of creating linked anolyte-catholyte materials for RFBs.

Daniel graduated with a Chemistry degree from Central Michigan University this spring, and joined us for the summer before he started at Michigan State University in East Lansing to study a Masters in Chemical Engineering.  Daniel has a very bright future and he will be great at anything he wants to do.  We appreciate that you spent the summer with us Daniel!

Novel Dendrimer synthesis for use in non-aqueous redox flow batteries

Alexandra Glennon, Dennis Downing and Dr. Thomas Guarr

This research is focused on nonaqueous flow batteries, specifically the membrane barrier which acts as a wall keeping the electrolyte solutions separate.  Nonaqueous batteries can contain a membrane which is less expensive than those in aqueous batteries, but it is not as ‘flow-proof’, meaning that molecules can still travel through it if small enough.  A possible solution to this problem is dendrimers.  Dendrimers are tree-like molecules with multiple ‘branches’ that can be attached to molecules to make them larger while also increasing electron density.  This larger molecule then inhibits the electrolytes’ ability to move through the membrane barrier separating the electrolytic solutions, allowing only the electrons in the solution to cross over and creating a flowing electrochemical battery.  the dendrimer used in this research was attached to pyryliums in order to increase molecular size and then analyzed through mass spectrometry, proton NMR, TLC, cyclic voltammetry and differential pulse voltammetry.  Currently, pyridinium compounds are being synthesized in hopes to make additional dendrimers with them.

Alex completed the third year of her Chemistry degree at the University of Iowa before she came to try out research with us this summer.  She enjoyed Holland and is interested in future battery research at U of Iowa.  She is completing her final year and we are excited to find out what she does when she graduates next year.