Tandem Catalysis Overcomes the Rate-Determining Sulfur Conversion Cascade in Na─S Batteries

Room-temperature sodium-sulfur (RT Na─S) batteries offer high theoretical energy density and low cost, yet their practical performance is fundamentally limited by sluggish sulfur redox kinetics, particularly the intertwined kinetic limitations of late-stage Na₂S₄→Na₂S₂→Na₂S conversions. Here, we propose a step-targeted tandem catalysis strategy that integrates atomically dispersed Fe-N₄ sites with polar ZrO₂ nanodomains within a conductive carbon host to precisely regulate the rate-determining sulfur conversion cascade. Density functional theory reveals a step-specific catalytic sequence, in which Fe-N₄ preferentially lowers the activation barrier for Na₂S₄→Na₂S₂ conversion, while ZrO₂ thermodynamically drives the subsequent Na₂S₂→Na₂S step. Their electronic coupling creates a continuous activation landscape that accelerates the entire solid-solid reaction cascade. Experimental kinetic analyses corroborate this mechanism, showing reduced polarization, enhanced surface-controlled kinetics, and mitigated transport limitations. As a result, the tandem-catalyzed Na─S cathode delivers an initial capacity of 1408 mAh g^-1, ultralong cycling stability over 10 000 cycles at a high current density of 5 A g^-1, and robust operation at -20°C. This work establishes tandem catalysis as an effective design paradigm for precisely regulating multistep sulfur conversion reactions in Na─S batteries.