Revalidating KCrPDTA for aqueous redox flow batteries

Inconsistent reporting practices and single-cell performance claims complicate the comparison of redox flow battery electrolytes across laboratories. Reproducing reported performance metrics for KCrPDTA-based batteries proved challenging, motivating systematic revalidation of KCrPDTA synthesis and characterization, and testing in cells. We identify three compounding variability sources: (i) hydration state inconsistencies in isolated KCrPDTA introducing molar mass errors of up to 4% that propagate into state-of-charge calculations, (ii) impurities eliminated by selective KCrPDTA crystal isolation prior to complete evaporation of the reaction mixture, and (iii) cell assembly artefacts including membrane shorting which produces persistently low coulombic efficiencies unrelated to electrolyte properties. Using a standardized protocol across 22 fuel-cell-type KCrPDTA-K₄[Fe(CN)₆] cells, assembled by multiple operators using various material batches, we obtain reproducible average coulombic and energy efficiencies of 99.54 ± 0.08% and 86.3 ± 1.7% over 50 cycles to 80% nominal state-of-charge at 100 mA cm^-2, values that are statistically grounded in a way single-cell studies are not. Across four cell architectures, coulombic efficiency stays within 99.3 to 99.7% while energy efficiency ranges from roughly 80 to 89%, highlighting the impact of cell hardware on key performance metrics. To support transparent benchmarking, we share all underlying data in a machine-readable format with semantically annotated linked metadata, alongside an open-source analysis pipeline and a metadata reporting template.