Boosting the electrochemical properties of polysulfide by iron(Ⅱ) phthalocyanine and its mechanism

The sulfur/iron (S/Fe) redox flow battery (RFB) offers attractive attributes such as high safety, environmental compatibility, and low cost, making it a promising candidate for large-scale energy storage. However, its development is hindered by the sluggish kinetics of polysulfide reduction during charging. Herein, we report iron phthalocyanine (FePc) supported on graphite felt as a highly effective electrocatalyst for the S 4 2− /S 2 2− redox couple. The FePc-based S/Fe RFB achieves an energy efficiency of 67.9 % at 120 mA/cm 2 and exceptional stability over 1000 cycles. Electrochemical analysis shows enhanced kinetics, with a higher exchange current density and a lower Tafel slope (76.5 mV dec −1 ) compared to the blank electrode (388.6 mV dec −1 ). The full cell delivers a peak power density of 206.4 mW/cm 2 and maintains over 75 % energy efficiency at 80 mA/cm 2 . Combined experimental and theoretical results reveal that FePc preferentially stabilizes polysulfide via middle-sulfur adsorption, facilitates S–S bond elongation, and promotes electron transfer. The insights gained into the catalytic role of FePc in polysulfide conversion provide a foundation for designing high-performance, durable, and cost-effective RFBs.