In the relentless quest for sustainable and reliable energy storage solutions, flow batteries have emerged as one of the most promising contenders. These systems offer remarkable safety and scalability, key properties that are indispensable for integrating renewable energy into the power grid efficiently. Among various flow battery chemistries, zinc/bromine (Zn/Br) flow batteries have attracted widespread attention, primarily due to their high energy densities and cost-effective electrolyte components. Yet, the widespread adoption of Zn/Br flow batteries has been significantly hindered by their limited service life and the environmental challenges posed by bromine’s corrosive and volatile nature.
A groundbreaking advancement has now been unveiled by a team of researchers who introduced an innovative strategy that remarkably extends the lifespan and enhances the environmental profile of Zn/Br flow batteries. By identifying sodium sulfamate (SANa) as a robust bromine scavenger and incorporating it directly into the catholyte, the team significantly mitigated the concentration of free bromine (Br₂), keeping it low at around 7 millimolar. This reduction not only curtails the hazardous effects associated with bromine volatility and corrosion but also promises to revolutionize flow battery design by mitigating the intrinsic issues that have so far limited the technology’s full potential.
The key to this transformative development lies in the rapid and selective reaction of sodium sulfamate with bromine, yielding a stable and much milder intermediate: N-bromo sodium sulfamate (Br-SANa). This compound features a Br⁺ species that takes advantage of the chemical properties of bromine in a controlled fashion, suppressing the deleterious free bromine species while opening new avenues for enhanced electrochemical performance. Crucially, the researchers uncovered that the Br-SANa/Br⁻ redox pair engages in a two-electron transfer reaction, a significant departure from the traditional single-electron processes associated with bromine chemistry in flow batteries.
This multi-electron transfer mechanism directly translates to increased energy density. In fact, the new Zn/Br flow battery architecture demonstrated an unprecedented energy density of 152 watt-hours per liter, a sharp contrast to the roughly 90 watt-hours per liter achievable with conventional Zn/Br designs. This enhancement marks an important milestone in flow battery technology, positioning the system as a viable candidate for grid-scale applications where energy density and cycle life critically dictate economic viability and operational sustainability.
Another standout feature of the newly developed flow battery is its dramatically improved cycle life. Traditional Zn/Br flow batteries typically succumb to performance degradation after about 30 cycles, a major limitation for commercial viability. However, with the implementation of the sodium sulfamate scavenger and the resultant formation of Br-SANa, the researchers achieved over 600 stable charge-discharge cycles. This leap in durability offers a substantial reduction in maintenance, downtime, and operational costs, further solidifying this new approach as a breakthrough in the field.
Central to the success of this system is the integration of a sulfonated polyetheretherketone (sPEEK) membrane, which plays a critical role in facilitating ion transport while maintaining chemical stability in the corrosive bromine environment. The membrane’s robust properties complement the unique chemistry introduced by sodium sulfamate, enabling efficient ionic conduction without compromising the cell’s long-term integrity. This integration of membrane technology with chemical innovation underscores the multifaceted approach needed to tackle longstanding issues in flow battery development.
To validate their laboratory findings and demonstrate the technology’s scalability, the research team assembled a 5-kilowatt (kW) stack using their new design. This system functioned reliably for more than 700 cycles, equating to roughly 1,400 hours of operation, without any notable degradation or failure. This pragmatic demonstration underscores the real-world applicability of the new Zn/Br flow battery chemistry for large-scale renewable energy storage, which is essential to buffering the intermittency of sources like solar and wind power.
The implications of this work extend beyond just performance enhancements. By capturing bromine in a chemically stable, low-volatility compound, the environmental footprint of Zn/Br flow batteries is drastically reduced, addressing important safety and ecological concerns. This positions the battery technology as a truly green and sustainable solution, in harmony with the overarching goals of clean energy integration and carbon neutrality efforts worldwide.
The researchers’ discovery not only paves the way for more durable and efficient Zn/Br batteries but also opens up exciting possibilities for exploring other chemical scavengers and multi-electron transfer reactions in electrochemical energy storage. The strategy of employing a bromine scavenger fundamentally changes how reactive intermediates in flow batteries can be managed, potentially inspiring a new class of high-performance batteries that combine safety, energy density, and longevity.
Moreover, the synthesis and implementation of N-bromo sodium sulfamate (Br-SANa) as a stable intermediate offers insights into bromine chemistry that could be leveraged in various other chemical and industrial processes, especially those requiring controlled bromine reactions. The ability to tame bromine’s inherent reactivity without sacrificing electrochemical performance highlights how molecular engineering can solve complex practical challenges in battery technologies.
This research also exemplifies the importance of interdisciplinary collaboration, combining electrochemistry, materials science, and chemical engineering disciplines to engineer a solution that was elusive for decades. Each aspect, from membrane design to electrolyte chemistry modification, was carefully optimized, proving that tackling energy storage challenges requires a holistic approach.
As grid-scale renewable energy integration accelerates globally, flow batteries like the one developed here offer an ideal pathway to energy storage that meets the demands of high capacity, safety, and sustainability. This advancement in Zn/Br flow battery technology, backed by multi-electron transfer chemistry, sets a new benchmark for the field, charting a path toward widespread adoption and impact.
In conclusion, the introduction of sodium sulfamate as a bromine scavenger in Zn/Br flow batteries represents a landmark innovation that addresses the core limitations of this promising technology. The enhanced energy density, extended cycle life, improved safety profile, and environmental sustainability together mark a paradigm shift, potentially revolutionizing how energy is stored at grid scale. As researchers continue to optimize and scale this technology, the future of renewable energy storage looks more accessible, durable, and environmentally friendly than ever before.
Subject of Research: The development of a corrosion-free, high-energy-density zinc/bromine (Zn/Br) flow battery enabled by incorporating a bromine scavenger and multi-electron transfer chemistry.
Article Title: Grid-scale corrosion-free Zn/Br flow batteries enabled by a multi-electron transfer reaction.
Article References:
Xu, Y., Li, T., Peng, Z. et al. Grid-scale corrosion-free Zn/Br flow batteries enabled by a multi-electron transfer reaction. Nat Energy (2025). https://doi.org/10.1038/s41560-025-01907-5
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