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Quantitative Solid-Liquid Matching and Capacity Optimization of Prussian Blue Redox Targeting in Neutral Iron-Sulfur Flow Batteries

 

  • Jiake Zhang 1,†,   
  • Yuzhuo Qi 1,†,   
  • Xiaokun He 1,2,   
  • Zhuo Li 1,   
  • Qiang Ma 1,   
  • Huaneng Su 1,   
  • Puiki Leung 3,   
  • Qian Xu 1,*

Received: 19 Jul 2026 | Revised: 13 Aug 2026 | Accepted: 31 Aug 2026 | Published: 16 Sep 2026

Abstract

Neutral iron-sulfur flow batteries feature low cost, high safety and environmental friendliness, demonstrating great application potential for large-scale energy storage. However, their cathodic capacity is fundamentally limited by the low solubility of ferricyanide active species. Most previous works merely verified the reversible redox reaction between Prussian blue (PB) and ferrocyanide in symmetric single-electrolyte cells, without systematic quantitative research on solid-liquid matching mechanisms and practical full-cell performance evaluation in iron-sulfur systems. This study explores cathode capacity enhancement and full-cell electrochemical characterization to solve the above bottleneck. Nickel sulfide modified graphite felts were synthesized via an in-situ hydrothermal route, and a redox-targeted symmetric cell was assembled with ferricyanide mediators and solid PB. CV results reveal favorable potential matching, while XRD measurements confirm the reversible phase transition between PB and Prussian white (PW) during cycling. The 0.3 M ferricyanide electrolyte achieves effective PB activation, and among 10–40% addition ratios, the 20% PB loading delivers the optimal capacity increment and material utilization, yielding a maximum discharge capacity of 69.66 mAh and a peak power density of 14.58 mW cm−2 in full-cell tests. Integrating 20% PB into full cells remarkably elevates coulombic, voltage and energy efficiencies, with voltage efficiency improved most prominently. Energy efficiency drops continuously as current density rises from 20 to 60 mA·cm−2. The battery reaches its maximum energy efficiency at 40 °C, since mild heating accelerates solid-liquid redox targeting kinetics without inducing PB lattice distortion or ferrocyanide hydrolysis.

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Zhang, J.; Qi, Y.; He, X.; Li, Z.; Ma, Q.; Su, H.; Leung, P.; Xu, Q. Quantitative Solid-Liquid Matching and Capacity Optimization of Prussian Blue Redox Targeting in Neutral Iron-Sulfur Flow Batteries  . Applied Energy Science 2026, 1 (1), 7.
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