A Tandem Electrocatalysis of Sulfur Reduction by Bimetal 2D MOFs

The diversity and coupling of sulfur redox intermediates and its associated solid-liquid-solid multiphase conversion mechanism pose great challenges in designing a proper electrocatalysts for Li-S batteries. In this report, it is proposed that an ideal catalyst should possess two catalytic centers which catalyze liquid-liquid conversion and liquid-solid conversion in tandem within one structure, with the use of 2D MOF nanosheets with different metal centers for validation. It is uncovered that the Ni-MOF is more effective in catalyzing the reduction of long-chain polysulfides, while Co-MOF benefits the Li2S deposition kinetics. Moreover, synergistic sulfur electrocatalytic activity for the integrated bimetal CoNi-MOF is witnessed. It greatly decreases the reaction activation energies, accelerates the faradaic current density for both of the reaction regions, and effectively inhibits the shuttle effect. This is attributed to charge redistribution between Ni and Co via bridge O in the MOF structure. The S@CoNi-MOF composite endows high reversible capacity (1450 mAh g(-1) at 0.1 C), enhanced cycling stability (500 cycles at 1 C with a low-capacity decay rate of 0.036% per cycle), and improved rate capability.

Automated summary

The study reveals that using catalysts synthesized with 2D MOF nanosheets with different metal centers can optimize the performance of Li-S batteries, where Ni-MOF effectively catalyzes the reduction of long-chain polysulfides, and Co-MOF benefits the deposition kinetics of Li2S. Furthermore, the bimetal CoNi-MOF exhibits synergistic sulfur electrocatalytic activity, reducing reaction activation energies, enhancing reaction rates, and effectively inhibiting the shuttle effect.