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

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 (Na₂Sₙ, n ≤ 4), which accumulate as insulating Na₂S/Na₂S₂. Herein, we report a Cu-MOF-derived microporous carbon bearing both carboxyl (COOH) and amide (CONH₂) groups (denoted MPC-Cu). The unique 0.5-0.8 nm uniform pores effectively physically lock S_2-4 molecules, eliminating long-chain polysulfides (Na₂Sₙ, 4 < n ≤ 8) shuttling. Density functional theory (DFT) calculations and electrochemical analysis confirm that COOH groups enhances Na₂Sₙ adsorption (binding energy -1.51 eV for Na₂S₄) and promotes Na⁺ diffusion (ranging from 10^-9-10^-11 cm² s^-1), whereas CONH₂ groups lower the Na₂S 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 NaS batteries.