Ligand exchange determines the catalytic activity of the sulfur reduction reaction in lithium-sulfur batteries

Homogeneous catalysts have great promise for accelerating the sulfur reduction reaction (SRR) and improving sulfur utilization in Li-S batteries without sacrificing energy density. We report that the d charge of the metal site in metal porphyrin (MTPP) catalysts, which is related to the ligand exchange ability by S species, is linearly correlated to the turn-over frequency (TOF) and apparent activation energy ( E a ) in the SRR. MnTPP with a d charge of 1.22 e results in a high TOF of \(37 \, {\rm mol}_{{\rm Li}_{2}{\rm S}} \, {\rm mol}_{\rm metal}^{-1} \, {\rm s}^{-1}\) for Li 2 S precipitation. Lithium-sulfur batteries assembled with the MnTPP catalyst had a low shuttle constant of 0.018 h −1 , as well as a high reversible capacity of 994 mAh g −1 at 1 C and a stable cycling performance with a low capacity decay per cycle of 0.08% after 500 cycles. This work establishes an electronic structure-activity relationship for porphyrin-based catalysts in SRR and provides a strategy for the design of homogeneous catalysts for Li-S batteries.