Generation of unpaired electrons to promote electron transfer at the cathode of room-temperature sodium sulfur batteries

[Display omitted] •Co3O4 nanoparticles supported on hollow tubular C3N4 nanostructures were obtained.•Design heterostructures to investigate the electron transfer mechanism.•This electron transfer shifts the spin state of Co from low to high.•Unpaired electrons transfer to sodium polysulfides, lowering the kinetic barrier.•The Co3O4-NC@C3N4/S cathodes demonstrate excellent electrochemical performance. Room-temperature sodium-sulfur batteries offer significant potential for energy storage, but they are hindered by slow Na-S reaction kinetics. While trial and error screening shows cobalt-based sulfur hosts to effectively activate this reaction, this study aims to enable a more rational catalyst design by exploring how cobalt’s electronic configuration within the cathode composite affects its activity and how this configuration can be adjusted through charge injection from neighboring atoms. Cobalt oxide nanoparticles coated with carbon nitride serve as a model system for this purpose, where N atoms in C3N4 donate electrons to Co, generating additional unpaired Co 3d electrons, that are then transferred to sodium polysulfides with a reduced kinetic barrier. Experimental and theoretical analyses reveal that this activated electronic state boosts charge transfer, while the adjusted d-band center improves adsorption energy, lowering the reaction energy barrier for the polysulfide conversion rate-determining step.