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A shared flow-battery cell and test brief did not make eight research groups’ electrochemical procedures identical. Josh Bailey’s account of an international interlaboratory effort highlights why published flow-battery results—especially polarisation curves—are difficult to compare without detailed protocols and setup descriptions.
Why researchers compared flow-battery tests
At the 2024 UK Flow Battery Network Annual Symposium, MIT researcher Fikile Brushett described how difficult it can be to reproduce performance metrics reported in the literature. Researchers from several institutions recognized the problem and set out to improve the reliability and accessibility of flow-battery testing.
Queen’s University Belfast and MIT joined researchers from Queen Mary University of London, Eindhoven University of Technology, Harvard University, the University of Cambridge, and the University of Manchester in an interlaboratory study. The eight groups used components of a common low-cost, 3D-printable cell designed by Hugh O’Connor, along with an assembly guide. They were asked to conduct charge–discharge cycling, polarisation curve analysis, and electrochemical impedance spectroscopy. Some parameters were prescribed; others were left to each group. The researchers later collected procedures and data through a survey. Bailey’s account in Chemistry World, published 1 June 2026, describes the effort and its results.
What varied across the laboratories
Polarisation curves depended on the protocol
Every one of the eight groups used a slightly different polarisation-testing protocol. That matters because a polarisation curve is not just a property of the cell: the procedure used to measure it affects the result. Bailey’s account therefore cautions against comparing published curves when the methods are not explicitly reported, and argues for a standardised approach comparable to those used in fuel-cell and electrolyser testing.
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Cycling showed measurable variation
The groups’ charge–discharge procedures were largely similar, but the study still reported variability of ±9.2% in electrolyte utilisation and ±2.5%/day in capacity decay. These figures are those reported in Bailey’s 2026 account; they describe variation in this study, not universal expected performance ranges for flow batteries.
Impedance results differed despite a shared model
Electrochemical impedance spectroscopy results spanned a wide range of area-specific resistance values for ohmic, charge-transport, and mass-transport losses, even though the groups used the same equivalent-circuit model. A shared model alone therefore did not make the reported resistance values consistent.
The eight-group study could not unequivocally attribute the differences between groups to measured participant variability. The findings identify reproducibility and reporting problems; they do not establish that one particular setup choice caused all the observed variation.
Setup details that may contribute to variation
Survey responses drew attention to electrical connections and electrolyte-tank configuration. Follow-up investigations by the two leading institutions examined two- and four-point probe connections, cable length, tube placement, and stirring. Bailey reports that poor electrical connections may account for an appreciable proportion of variable ohmic losses. Tubing that allows fluid to bypass part of the tank may affect electrolyte utilisation, at least when the electrolyte is not stirred.
These are plausible contributors, not a complete causal explanation of the interlaboratory results. The practical value is that they are controllable details worth documenting and checking rather than assuming a common cell design makes them equivalent.
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Five practical steps for more reproducible tests
- Use a four-point probe connection. Keep connectors clean and firmly attached to the current collectors.
- Stir the electrolyte where possible. Mixing can promote homogeneity and mitigate possible effects of fluid bypass; it is a setup consideration, not a universal fix.
- Separate inlet and outlet tubing. This is particularly important when stirring is not possible.
- Report the exact electrochemical protocol. Give the procedure used for polarisation curves and other electrochemical measurements, rather than relying on a general test label.
- Describe the whole setup and chosen parameters. Include enough detail about connections, tubing, electrolyte handling, and test conditions for another laboratory to reproduce the work.
What the study means when comparing published results
When evaluating flow-battery data from different papers, first check whether the measurements were made using comparable procedures—not merely whether the same type of cell or equivalent-circuit model was used. For polarisation curves, look for the exact protocol. For cycling and impedance data, consider the reported setup and parameters, including electrical connection configuration, electrolyte mixing, and tubing layout.
Bailey reported that a larger follow-up study involving almost 40 researchers worldwide was underway when his article was published on 1 June 2026. That is a publication-time status, not confirmation of the study’s present status.
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The account cites the underlying study as H. O’Connor et al., Energy & Environmental Science (2026), 19, 3323, DOI 10.1039/d5ee07103h.
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