Harnessing functional groups in microporous carbon catalysts for accelerated sulfur redox in room temperature NaS batteries

Microporous carbons are promising sulfur hosts for room temperature sodium–sulfur (RT Na–S) batteries. Yet, most designs primarily focus on confining small S 2 – 4 molecules and overlook the sluggish redox of short-chain polysulfides (Na 2 S ₙ ,  n  ≤ 4), which accumulate as insulating Na 2 S/Na 2 S 2 . Herein, we report a Cu-MOF-derived microporous carbon bearing both carboxyl ( COOH) and amide ( CONH 2 ) groups (denoted MPC-Cu). The unique 0.5–0.8 nm uniform pores effectively physically lock S 2 – 4 molecules, eliminating long-chain polysulfides (Na 2 S ₙ , 4 <  n  ≤ 8) shuttling. Density functional theory (DFT) calculations and electrochemical analysis confirm that COOH groups enhances Na 2 S ₙ adsorption (binding energy −1.51 eV for Na 2 S 4 ) and promotes Na + diffusion (ranging from 10 −9 –10 −11  cm 2  s −1 ), whereas CONH 2 groups lower the Na 2 S oxidation barrier from 1.16 eV to 0.70 eV. Consequently, S/MPC-Cu cathode delivers long-term cycle performance (571.5 mAh g −1 at 2 A g −1 with a capacity retention of 83 % over 1000 cycles) and outstanding rate performance (504.1 mAh g −1 at 5 A g −1 ). This work provides a novel strategy in designing microporous carbon catalysts for cathodes of high-capacity, long-life RT Na S batteries.