Deciphering the contributing motifs of reconstructed cobalt (II) sulfides catalysts in Li-CO 2 batteries.

Developing highly efficient catalysts is significant for Li-CO 2 batteries. However, understanding the exact structure of catalysts during battery operation remains a challenge, which hampers knowledge-driven optimization. Here we use X-ray absorption spectroscopy to probe the reconstruction of CoS x (x = 8/9, 1.097, and 2) pre-catalysts and identify the local geometric ligand environment of cobalt during cycling in the Li-CO 2 batteries. We find that different oxidized states after reconstruction are decisive to battery performance. Specifically, complete oxidation on CoS 1.097 and Co 9 S 8 leads to electrochemical performance deterioration, while oxidation on CoS 2 terminates with Co-S 4 -O 2 motifs, leading to improved activity. Density functional theory calculations show that partial oxidation contributes to charge redistributions on cobalt and thus facilitates the catalytic ability. Together, the spectroscopic and electrochemical results provide valuable insight into the structural evolution during cycling and the structure-activity relationship in the electrocatalyst study of Li-CO 2 batteries.