Chemical Used for Water Treatment Could Find Application in Iron-based Flow Batteries

The safe, economical, water-based flow battery is made with earth-abundant materials


Researchers at the U.S. Department of Energy’s (DOE) Pacific Northwest National Laboratory (PNNL) have repurposed nitrogenous triphosphate or nitrilotri-methylphosphonic acid (NTMPA), which is commonly used in water treatment facilities, for large-scale battery energy storage.

In the study published in the Nature Communications journal, the researchers said their lab-scale, iron-based battery exhibited remarkable cycling stability over 1,000 consecutive charging cycles while maintaining 98.7% of its maximum capacity.

Since the 1980s, iron-based flow batteries have been conventionally used for large-scale energy storage and are currently commercially viable. However, the researchers developed a method to store energy in a unique liquid chemical formula that combines charged iron with a neutral-pH phosphate-based liquid electrolyte or energy carrier.

In addition to enabling a pathway for a safe, economical, water-based flow battery made with earth-abundant materials, this discovery also offers a way to incorporate intermittent energy sources such as wind and solar energy into the electric grid.

City planners face consumer safety concerns as grid operators attempt to locate battery energy storage systems near energy consumers in urban and suburban areas. This new aqueous flow battery reported in the study could alleviate those concerns.

Flow batteries consist of two chambers, each filled with a different liquid, and the batteries charge through an electrochemical reaction and store energy in chemical bonds. Connection to an external circuit causes them to release that energy, which can further power electrical devices.

As they can serve as backup generators for the electric grid, flow batteries remain one of the key pillars of decarbonization strategies involving renewable energy storage.

According to the authors, a BESS facility using chemistry similar to what they have developed would have the added advantage of operating in water at neutral pH. Further, this newly developed system also uses commercially available reagents that haven’t been previously used or investigated for flow batteries.

Iron-based Flow Batteries

The team’s initial design can reach the energy density of nearly 9 watt-hours per liter (Wh/L). At 25 Wh/L, vanadium-based systems are more than twice energy dense in comparison. While higher energy density batteries can store more energy in smaller square footage, a system fashioned out of earth-abundant materials could be scaled to provide the same energy output.

The team is now looking to improve battery performance by focusing on ion aspects, such as voltage output and electrolyte concentration, to increase energy density. The team has identified their voltage output to be lower than the typical vanadium flow battery output and is currently attempting to improve that.

The efforts to scale this up will also happen at a new facility called the Grid Storage Launchpad, which will open up in PNNL this year and is aimed at accelerating the development of future flow battery technologies.

Last year, researchers at the same laboratory said they discovered that a widely used food and medicine additive could significantly enhance the capacity and longevity of a next-generation flow battery design.

In March 2024, the U.S. energy storage market was reported to have experienced growth at a breakneck pace in 2023, as installations across all segments increased by 90% year-over-year as the country added 8.7 GW of new energy storage capacity.