Simple lead-based catalyst strategy boosts efficiency of iron-chromium flow batteries

Researchers have developed a simple lead-based catalyst strategy that significantly improves the performance of iron-chromium redox flow batteries, a class of long-duration energy storage systems widely seen as promising for large-scale grid applications. By introducing lead chloride into the electrolyte and enabling a catalyst to form directly on the electrode surface during operation, the team was able to improve chromium reaction kinetics, suppress hydrogen evolution, and achieve markedly higher energy efficiency under demanding operating conditions.

Iron-chromium redox flow batteries have attracted sustained interest because they use relatively abundant materials, offer intrinsic safety advantages, and can be suitable for stationary storage of renewable electricity. That makes them attractive for supporting wind and solar power, where stored energy must often be delivered over long durations rather than in short bursts. Yet despite those advantages, the chemistry still faces a practical bottleneck: the chromium half-reaction is sluggish, and unwanted hydrogen evolution can compete with it during battery operation. Together, these issues reduce efficiency, increase losses, and make it harder for the technology to deliver stable long-term performance at high current densities.

In the new study, the researchers focused on whether the chemical environment of chromium ions could be improved through a simple electrolyte additive. They introduced PbCl2 into the iron-chromium flow battery electrolyte and used this additive to achieve in-situ electrodeposition of a lead-based catalyst. Rather than relying only on standard electrochemical measurements, the team combined experiments with molecular dynamics simulations to better understand how the additive behaves in the electrolyte and how the resulting deposited species influence battery reactions. They also used in-situ differential electrochemical mass spectrometry to monitor hydrogen evolution signals during operation, allowing them to directly track one of the most important parasitic reactions limiting battery performance.

The results indicate that the main benefit does not come from a broad change in the bulk electrochemical properties of the electrolyte itself. Instead, the improvement appears to be closely tied to what happens on the electrode surface after lead species deposit there. According to the paper, the combined effects of Pb and Pb(ClO3)2 help catalyze the Cr3+/Cr2+ redox reaction while also suppressing hydrogen evolution. That combination matters because it addresses both sides of the performance problem at once: it makes the desired chromium reaction easier to drive, while reducing the competing reaction that wastes energy and undermines battery efficiency. The in-situ gas monitoring data further supported this picture by showing a clear inhibition of hydrogen evolution after the additive strategy was applied.

Performance gains reported in the study were substantial. The authors found that adding 40 mM Pb2+ significantly reduced reaction overpotential and raised the battery's energy efficiency to 83.90% at a current density of 140 mA/cm2. That compares with 78.22% for the original electrolyte, corresponding to an improvement of 5.68%. Just as importantly, the battery maintained stable operation for 400 cycles under those same conditions. In the context of iron-chromium flow batteries, that combination of efficiency, current density, and cycling stability is notable because it points to a practical route for making the chemistry more competitive without introducing a highly complex redesign of the full battery system.

The work also helps clarify an important mechanistic question for the field. The authors conclude that the additive's influence is mainly due to electrochemical deposition on the electrode surface rather than a major alteration of the electrolyte's intrinsic electrochemical behavior. That distinction could guide future optimization efforts, because it suggests that researchers may be able to improve battery operation by deliberately engineering catalytic interfaces instead of focusing only on bulk electrolyte formulation. In that sense, the study offers not just a performance improvement, but also a clearer framework for understanding how electrode-surface chemistry can be tuned to support chromium redox kinetics in practical devices.

If the approach proves scalable, it could help strengthen the case for iron-chromium flow batteries in large stationary energy storage systems, where low cost, long life, and operational safety are especially important. A simpler, cost-effective method for improving efficiency at relatively high current density could be valuable for renewable integration and grid balancing, where performance losses can have significant system-level consequences. At the same time, the researchers' results should still be interpreted within the scope of the reported experimental configuration. Further work will be needed to assess how the lead-based catalyst strategy performs under broader operating conditions, over longer lifetimes, and in larger battery systems. Even so, the study suggests that in-situ catalyst formation may be a practical and effective way to unlock better performance in iron-chromium redox flow batteries.

Reference

Author:

Yingchun Niu ^a , Wenjie Lv ^{a b} , Yinping Liu ^a, Ziyu Liu ^a, Ruichen Zhou ^a, Xuan Zhou ^a, Weiwei Guo ^a, Wei Qiu ^a, Chunming Xu ^a, Quan Xu ^a

Title of original paper:

The effect of lead-based catalyst in-situ electrodeposition on the performance of iron-chromium redox flow batteries

Article link:

https://www.sciencedirect.com/science/article/pii/S2773153725000817

Journal:

Green Energy and Intelligent Transportation

DOI:

10.1016/j.geits.2025.100331

Affiliations:

^a State Key Laboratory of Heavy Oil Processing, China University of Petroleum (Beijing), Beijing 102249, China

^b Zhonghai Energy Storage Technology (Beijing) Co., Ltd, China

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