Recognizing the contrasting role of N, O dual-coordinated single-atom iron catalyst in Li−S and Al−S batteries

Single-atom catalysts (SACs) have been increasingly employed to promote the sluggish reaction kinetics of metal–sulfur (M–S) batteries. Nevertheless, the structure-property relationship between coordinating elements and catalytic properties remains unexplored by far. Herein, N, O dual-coordinated single-atom iron catalysts (Fe-NO-C) were exemplified to unravel the influence of coordinating oxygen on catalytic efficiencies for lithium–sulfur (Li–S) and aluminum–sulfur (Al–S) batteries. Doping of high electronegative oxygen depressed the d-p hybridization of Fe-NO-C towards sulfur species as well as its catalytic activities for Li–S batteries. Interestingly, an opposite effect of coordinating oxygen was predicted in Al–S batteries. The inefficient d-p hybridization stabilized aluminum polysulfides on Fe-NO-C through dipole-dipole interactions, which accelerated Al–S conversion kinetics and improved the bidirectional catalytic performance. These findings enabled noncovalent interaction to be alternative way to access desirable catalytic effect. Guided by these design principles, advanced Al-S batteries using S@Fe-NO-C cathode exhibited a high reversible capacity of 550.1 mAh g−1 after 400 cycles and excellent high-rate capability of 352.1 mAh g−1 at 3 A g−1. This work provides valuable insights into the understanding of coordination structures of SACs and paves the way for developing superior catalysts in M–S applications.