Optimizing Solubility and Stability of 2,6-Diethyl-4-(4-Methoxyphenyl)pyridinium Compounds for Redox Flow Batteries

Margaret Cooper, Madison Shaffer, Thomas Guarr

As the demand for renewable energy grows, the need for long duration energy storage has become critical.  Redox flow batteries (RFBs) have emerged as a potential alternative for grid-scale energy storage as they are both safe and environmentally friendly.  RFBs employ two electrolyte solutions (an anolyte and catholyte) and achieving commercially viable energy density in such systems requires that the anolyte displays a low reduction potential and high solubility.  Previous research has shown that pyridinium compounds offer low reduction potentials, but varying solubilities and stability in their reduced states.  This work focuses on 2,6-diethyl-4-(4-methoxyphenyl)pyridinium compounds with various 1-aryl substituents in an attempt to improve solubility and stability while maintaining a low reduction potential.  These compounds are prepared via condensation of 2,6-diethyl-4-(4-methoxyphenyl)pyrylium with the desired aryl amine.  Solubilities were measured by UV-visible spectroscopy, while radical stability was measure by cyclic voltammetry.

Maggie attends Montana State University and we were lucky to have her join us at the OESLab in Holland this summer.  She is a lot of fun to have around and she is up for anything, including a lot of synthesis projects and analysis. Thanks for being a trooper!  Enjoy the rest of your summer and enjoy returning to Big Sky country!

Analysis of Diffusion Coefficient Data using Rotating Ring Disk Electrode for Symmetric Non-Aqueous Redox flow Batteries

Nathan Barr and Thomas Guarr

As the world becomes more electrically focused, the resources needed for manufacturing batteries are in lower supply, and the collection of raw materials causes adverse effects on the environment.  Due to this, interest in more sustainable batteries, such as nonaqueous redox flow batteries (RFBs), has dramatically increased.  Recent research efforts have focused on improving the energy density and power density, two key measures of battery performance.  In RFBs, these two parameters depend on numerous factors, including the solubility, redox potential, electron transfer kinetics, and diffusion coefficient of the active material.  Previous work in our lab demonstrated a wide range of pyridinium electrolyte redox potentials, as well as the ability to drastically alter their solubilities through minor structural modification.  This work presents diffusion coefficient data of a structurally diverse set of pyridinium salts using a rotating ring-disk electrode (RRDE), with the goal of analyzing how different functional groups may have positive or negative effects on the diffusion coefficient, and how these pyridiniums can be modified to achieve greater stability in the reduced state without sacrificing other important attributes.

Nate is studying Chemical Engineering at Calvin University.  I always appreciate having an engineer to contrast with our chemists and Nathan did not disappoint!  He brought a lot of enthusiasm to his project and made some very interesting and unexpected discoveries.  Nate is thoughtful and thorough with his experiments and we really enjoyed having him in the lab to counteract our synthesis-heavy summer.

Increasing the Energy Density of Redox Flow Batteries Using Pyridinium Compounds Displaying Two Reversible Reductions

Sophia Valdivia, Madison Shaffer, Andrii Varenikov, Thomas Guarr

Redox flow batteries (RFBs) are gaining interest to make energy storage more affordable and efficient.  RFBs are an energy storage device that relies on the oxidation and reduction of soluble electroactive chemical species for charging, storing, and discharging energy.  Redox-active organic molecules (ROMs) are promising electroactive materials due to their low production costs, low molecular weights, and the ability to achieve significant electrochemical potential differences between the anolyte and catholyte.  Previous research has shown that pyridiniums with 1-electron systems provide reduction potentials between -1.5 V and -1.8 V, but they were not sufficiently stable.  This work aims to increase the battery’s energy density by synthesizing a pyridinium with a 2-electron system while stabilizing the first reduction.  Using cyclic voltammetry, the reduction potential is determined, and insight is gained about the stability of the radical.

Sophia first heard about our lab when Tom Guarr visited his alma mater, Benedictine College, to give a talk about his research.  She attends Benedictine in Kansas, but she is from Texas and she had never been to Michigan before.  She was very interested, applied, got accepted, packed up and came to Holland for the summer.  She did some great synthesis work and we loved having her here!  Thanks to Benedictine for sharing her.

Increasing Electrochemical Versatility by Linking Ferrocene to Pyridinium Salts

Riley Clark, Madison Shaffer, Thomas Guarr

Flow batteries have become increasingly popular due to their increased lifespan and ethical sourcing of raw materials.  While aqueous flow batteries have been studied for decades, nonaqueous organic flow batteries are generating new interest because of their higher cell voltages, greater structural diversity, and low manufacturing costs.  This work focuses on linking ferrocene catholytes to pyridinium anolytes to produce molecular systems that can be both reduced and oxidized.  By using this approach, the expensive ion-selective membrane normally used in flow batteries can be replaced with a simple, inexpensive porous separator.  Numerous synthetic pathways to such compounds have been explored, however the most promising of these involves the synthesis of substituted nitrophenyl ferrocenes via Suzuki coupling, followed by the reduction to produce an amine, and finally condensing the ferrocenyl amines with a pyrilium salt.  Further work involves testing the electrochemical properties, solubility, and stability of these compounds.

Riley is our first highlighted intern and she comes to us from Clemson University.  One of her mentors there was a former intern of ours and she came to us highly recommended.  Riley did some great synthesis work and her accomplishments are even more amazing when you consider she has only completed one year of undergrad!  We appreciate that she spent her summer with us when most people her age are working summers part-time scooping ice cream or something.  You are a very impressive person, Riley!  When the winter gets too long up here, we are going to take a field trip to South Carolina to visit.

Thanks again to Hope College for inviting us participate in the 2024 Chemistry Summer Symposium.  Our group presented 6 posters and 1 talk.  We enjoyed all of it!

Summer isn’t over yet, but I want to talk about all the great things that have been happening since my last post.  We are so fortunate here at the OESLab to enjoy so many different, fun and interesting people that come through the lab.  This summer is certainly no exception!  I will highlight each intern in future posts, but here are some fun pics of the group…

We are so excited about welcoming our summer interns soon!  Below are the six (6!) contributors this summer.  Stay tuned for summer fun and research results!

Nathan Barr – Calvin College

Riley Clark – Clemson University

Maggie Cooper – Montana State University

Sophia Jaeger – Michigan Tech University

Avery Reimink – Hope College

Sophia Valdivia – Benedictine College

The lab is waiting for you 🙂

Madison and Tom spent a few days in sunny New Orleans at the ACS conference.

Madison presented a poster, connections were made and old friends were reacquainted…

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If you have been paying attention you have seen Dennis’ name and picture pop-up on our research posts this past summer.  Dennis joined us this spring and has been a valuable addition to our research team.  He was a terrific mentor to our summer students and has enthusiastically embraced the lab’s research.  We are lucky to have him!

Dennis has an extensive resume, here are a few highlights:

• Alum of Saginaw Valley State
• Has worked at Dow, MSU, Pfizer, New Holland Brewing, Amway and GM
• Has extensive research experience including dendrimers, carbohydrates, and neuroreceptors
• Has supervised, researched, developed, qualified, targeted, created, distilled, guided, quality engineered, and managed many, many projects over his career

Thank goodness he is here now working with us.  His experience and insights are valuable and his guidance for our future researchers is second-to-none.  We appreciate you Dennis!

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.