A team of researchers from Northwestern University has converted an organic industrial waste product into an effective storage agent for sustainable energy solutions that may eventually be used on much larger scales. The Journal of the American Chemical Society published the study.
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Metals like lithium and cobalt, obtained through intrusive and intensive mining, are necessary for the batteries that power phones, gadgets, and even automobiles. Moving away from metal-based solutions will support the green energy transition as more products rely on battery-based energy storage systems.
Initially considered a waste molecule, triphenylphosphine oxide is now being explored and utilized in various versions of redox flow batteries for grid-scale applications.
Many organic industrial synthesis processes, such as certain vitamins, produce thousands of tons of the well-known chemical byproduct annually, but after production, it is rendered useless and needs to be carefully disposed of.
According to the study, a “one-pot” reaction enables chemists to transform TPPO into a useful product with significant energy storage potential, paving the way for the feasibility of waste-derived organic redox flow batteries, a long-envisioned battery type.
Battery research has traditionally been dominated by engineers and materials scientists. Synthetic chemists can contribute to the field by molecularly engineering an organic waste product into an energy-storing molecule. Our discovery showcases the potential of transforming waste compounds into valuable resources, offering a sustainable pathway for innovation in battery technology.
Christian Malapit, Northwestern University
Malapit is an Assistant Professor in the Department of Chemistry at Northwestern University's Weinberg College of Arts and Sciences.
Redox flow batteries currently make up a small portion of the battery market, but between 2023 and 2030, the market is predicted to grow by 15% to reach a global value of 700 million euros.
Redox flow batteries employ a chemical reaction to transfer energy between electrolytes, which store energy, as opposed to lithium and other solid-state batteries that store energy in electrodes. Despite their lower energy storage efficiency, redox flow batteries are regarded as far superior options for grid-scale energy storage.
Not only can an organic molecule be used, but it can also achieve high-energy density getting closer to its metal-based competitors along with high stability. These two parameters are traditionally challenging to optimize together, so being able to show this for a molecule that is waste-derived is particularly exciting.
Emily Mahoney, Ph.D. Candidate and Study First Author, Northwestern University
The group needed to find a method to enable electrons to firmly pack in the solution without gradually losing storage capacity to attain energy density and stability. According to Mahoney, they “ran with it” after looking back and discovering a 1968 paper that described the electrochemistry of phosphine oxides.
The team then used static electrochemical charge and discharge experiments, akin to charging a battery, using it, and then charging it repeatedly, to assess the molecule's resilience as a potential energy-storage agent. The battery remained remarkably healthy after 350 cycles, gradually losing very little capacity.
This is the first instance of utilizing phosphine oxides a functional group in organic chemistry as the redox-active component in battery research. Traditionally, reduced phosphine oxides are highly unstable. Our molecular engineering approach addresses this instability, paving the way for their application in energy storage.
Christian Malapit, Northwestern University
The team hopes other researchers will take up the task and start collaborating with TPPO to further enhance and maximize its potential in the interim.
The study was funded by a start-up grant from Northwestern, the Department of Energy’s Office of Basic Energy Sciences, and the National Science Foundation Graduate Research Fellowship.
Journal Reference:
Mahoney, E. R., et al. (2025) Triphenylphosphine Oxide-Derived Anolyte for Application in Nonaqueous Redox Flow Battery. Journal of the American Chemical Society. doi.org/10.1021/jacs.4c07750.