Synergistically boosting the anchoring effect and catalytic activity of MXenes as bifunctional electrocatalysts for sodium-sulfur batteries by single-atom catalyst engineering.

MXene based sulfur hosts have attracted enormous attention in room temperature sodium-sulfur (RT Na-S) batteries due to their strong affinity towards soluble sodium polysulfides (NaPSs). However, their electrocatalytic performance needs further improvement. Here, a series of single non-noble transition metal (TM = Fe, Co, Ni, and Cu) atoms anchored on TiCS (TM@TiCS) were proposed as bifunctional sulfur hosts for Na-S batteries. The results testify that the introduction of TMs dramatically enhanced the chemical interaction between sulfur-containing species and TiCS, which is attributed to the co-formation of TM-S and Na-S covalent bonds. Importantly, compared with pristine TiCS, the sulfur reduction reaction (SRR) is thermodynamically more favorable on TM@TiCS. In addition, the incorporation of Fe, Co, and Ni atoms is also conducive to promoting the dissociation of NaS. The density of states (DOS) results suggest that TM@TiCS maintains metallic conductivity during the whole charge and discharge process. Overall, constructing single atom catalysts is an effective strategy to further improve the electrochemical performance of MXene based sulfur hosts for Na-S batteries.