A highly-efficient electrocatalyst for room temperature sodium-sulfur batteries: assembled nitrogen-doped hollow porous carbon spheres decorated with ultrafine α-MoC1-x nanoparticles

While room-temperature sodium-sulfur (RT Na-S) battery is considered one of the most promising technologies for next-generation energy storage, its commoditization is constrained by the shuttling and sluggish redox kinetics of the sulfur electrode. Herein, a honeycomb-like sulfur electrocatalyst with ultrafine alpha-MoC1-x nanoparticles uniformly distributed on nitrogen-doped hollow porous carbon spheres (MoC@NHC) is designed and synthesized. Prepared through a template-assisted strategy followed by a self-assembly and pyrolysis process, the interconnected hollow porous structure of MoC@NHC provides not only a microenvironment for confinement of sodium polysulfides (NaPSs) but also sufficient free space for accommodation of volume change during electrochemical cycling. Moreover, the polar alpha-MoC1-x nanoparticles coupled with N-doped carbon provides strong affinity to NaPSs and promote catalytic conversion of NaPSs, as confirmed by experimental results and theoretical calculations. Owing to the physical and chemical dual confinement effect and the fast conversion kinetics of NaPSs, the S/MoC@NHC-15 cathode demonstrates good rate performances (351.8 mAh g(-1) at 10 C) and outstanding cyclability (retaining capacities of 418.4 and 312.6 mAh g(-1) after 1000 cycles at 1 and 5 C, respectively). This study introduces a simple and effective method for fabrication of S/MoC@NHC cathode materials for high-performance RT Na-S batteries.