Electronic Spin State Determines Bidirectional Catalysis of Dual-Atom Catalysts in Sulfur Cathodes

The electronic spin state of metal atomic catalysts is pivotal in determining their catalytic activities. However, such catalysts that are prepared via conventional synthetic approaches often suffer from poorly defined coordination environments, which create challenges in precisely controlling their electronic spin configurations. Herein, we show that a CoFe dual-atom catalyst featuring coordinatively asymmetric FeN₂ and CoN₃ sites with a fixed coupling distance can be synthesized using a conjugated microporous polymer (designated as CoFe-CMP) and then demonstrate that the catalyst promotes the key reactions underlying both charging and discharge processes of sulfur cathodes. Experimental and theoretical data reveal that the Fe atoms adopt a high-spin state (S = 3/2) and the Co atoms assume a low-spin state (S = 1/2). The former configuration enhances electronic coupling with polysulfides, while the latter promotes the diffusion of Li atoms that are released upon Li₂S degradation. Collectively, these processes facilitate the interconversion between polysulfides and Li₂S, which are critical for optimizing lithium-sulfur (Li-S) battery operation. Li-S cells containing CoFe-CMP as the sulfur host exhibit outstanding performance in terms of specific capacity (1487 mAh g⁻¹ at 0.1 C), rate capacity (676.3 mAh g⁻¹ at 5 C), and cycling stability (a specific capacity of 499.2 mAh g⁻¹ is measured after 300 cycles at 0.2 C). This research provides a general methodology for tuning the electronic spin states of metal atomic catalysts, as well as guidance for adapting these catalysts for use in other applications.