Efficient Reversible Conversion between MoS2 and Mo/Na2 S Enabled by Graphene-Supported Single Atom Catalysts.

Sodium-ion batteries (SIBs) based on conversion-type metal sulfide (MS) anodes have attracted extraordinary attention due to relatively high capacity and intrinsic safety. The highly reversible conversion of M/Na2 S to pristine MS in charge plays a vital role with regard to the electrochemical performance. Here, taking conventional MoS2 as an example, guided by theoretical simulations, a catalyst of iron single atoms on nitrogen-doped graphene (SAFe@NG) is selected and first used as a substrate to facilitate the reaction kinetics of MoS2 in the discharging process. In the following charging process, using a combination of spectroscopy and microscopy, it is demonstrated that the SAFe@NG catalyst enables an efficient reversible conversion reaction of Mo/Na2 S→NaMoS2 →MoS2 . Moreover, theoretical simulations reveal that the reversible conversion mechanism shows favorable formation energy barrier and reaction kinetics, in which SAFe@NG with the Fe-N4 coordination center facilitates the uniform dispersion of Na2 S/Mo and the decomposition of Na2 S and NaMoS2 . Therefore, efficient reversible conversion reaction MoS2 ↔NaMoS2 ↔Mo/Na2 S is enabled by the SAFe@NG catalyst. This work contributes new avenues for designing conversion-type materials with an efficient reversible mechanism.