Researchers at Case Western Reserve University are addressing this challenge by developing novel electrolytes, the ion-conducting fluids at the heart of rechargeable flow batteries, that are designed for large-scale stationary storage applications while remaining nonvolatile and safer to handle.
Flow batteries operate in a manner similar to fuel tanks that can be scaled up as needed: the electrochemical cell stack functions as the engine, while the size of the external tanks holding the active materials determines how much energy the system can store, enabling designs that could power a neighborhood or small city for days or weeks without changing the core hardware.
The Case Western Reserve team has demonstrated a new class of structured electrolytes that are less prone to evaporation or ignition and that support a distinct mode of proton conductivity, allowing positively charged hydrogen ions to hop from molecule to molecule instead of physically drifting through the liquid.
According to the researchers, this hopping mechanism resembles a billiard ball ricochet at the molecular level, and it appears to enhance proton-coupled electron transfer reactions, improving how efficiently the electrolyte can move charge in a thick, viscous fluid that would normally hinder ion transport.
The work, carried out within the Breakthrough Electrolytes for Energy Storage Systems Energy Frontier Research Center at Case Western Reserve, and reported in Proceedings of the National Academy of Sciences, describes how the tailored electrolyte structure supports this Grotthuss-type transport and thus enables a completely new approach to designing large-scale batteries based on proton conduction.
By relying on proton hopping rather than the motion of large charged species, the electrolytes can remain thick enough to be stable and nonvolatile while still allowing high conductivity, an important safety advantage over conventional lithium-ion technologies whose organic electrolytes can catch fire if the cells overheat.
Conventional lithium-ion batteries, widely used in phones and laptops, shuttle lithium ions through organic electrolytes and store them at electrodes during charge and discharge; these flammable electrolytes limit their suitability and public acceptance for very large installations where failure could have serious consequences.
In contrast, the new electrolytes use hydrogen ions as the mobile charge carriers and are engineered so that the ions move by repeatedly shifting between hydrogen bonds in the liquid network, a process the team has mapped using a combination of experimental characterization techniques and computational modeling.
Lead researcher Burcu Gurkan, Kent Smith Professor II of chemical and biochemical engineering and director of the BEES2 Energy Frontier Research Center, said the group accepted that safer fluids would need to be relatively thick but shifted the design focus to letting tiny hydrogen ions hop across the molecular landscape instead of forcing bulky charged particles through a viscous medium.
Study coauthor Robert Savinell, the George S. Dively Professor of Engineering and founding director of the original BEES center, noted that this conductivity mechanism is far less sensitive to viscosity, so protons can move readily even when the solution remains dense and nonvolatile, maintaining safety without sacrificing performance.
The researchers emphasize that the technology is still at a development stage and that the current formulations do not yet offer the solubility and energy density needed for fully practical flow battery systems, making improved chemical solubility and higher storage density key goals for the next phase of work.
Beyond grid-scale batteries, the team expects that these structured electrolytes could also support other electrochemical technologies, including electrocatalytic processes that manufacture chemicals without the high pressures or temperatures common in traditional reactors, potentially lowering energy use and emissions in the chemical industry.
Research Report:Structured electrolytes facilitate Grotthuss-type transport for enhanced proton-coupled electron transfer reactions
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