Interfacial engineering with cationic electrocatalysts in aqueous polysulfide redox flow batteries

Polysulfide-based aqueous redox flow batteries (PSARFBs) suffer from intrinsic limitations in power density arising from the sluggish polysulfide reduction kinetics. Here, we reveal that this results from the inhibited polysulfide migration within the electric double layer (EDL) toward the negatively charged electrode. We introduce trace 1-ethyl-1-methylpyrrolidinium (EMP + ) as a cationic electrocatalyst, thereby significantly facilitating polysulfide migration and improving reduction kinetics by two orders of magnitude. EMP⁺ functions through reversible interfacial adsorption to shield local negative charge without chemical transformation, enabling sustained kinetic regulation. The developed polysulfide negolytes with EMP + demonstrated a stable electrochemical durability for 1,300 cycles/64.5 days and a high volumetric capacity of 100 Ah L negolyte −1 . PSARFBs employing 6 mM EMP + exhibited improved power capability at 150 mA cm −2 with 99.3% capacity delivery and a long cycle life of over 2,000 cycles and a decay rate of 0.000033%/cycle (0.0014%/day), establishing a mechanistic basis for improving power performance.