Crystal facet modification of hematite enabling effective polysulfide adsorption/conversion and improved LiS chemistry

Abstract

Crystal facet engineering has emerged as a highly effective method for boosting the catalytic performance of nanocrystalline catalysts. In this study, three hematite (α-Fe₂O₃) samples with distinct exposed facets were synthesized via solution synthesis and demonstrated strong chemical adsorption and catalytic properties, speeding up the redox reactions of sulfur species in lithium‑sulfur (LiS) chemistry. Among them, HEM-001 exhibited outstanding adsorption and catalytic performance attributed to the plentiful unsaturated coordinated oxygen atoms present on the (001) crystal facets. This specific facet not only facilitated the effective adsorption and conversion of polysulfides but also significantly lowered the decomposition energy barrier of Li₂S. The electrochemical cells utilizing these highly active electrocatalysts exhibited remarkable cycling stability, achieving a specific capacity of 846.8 mAh g⁻¹ after 200 cycles at 0.5C, and maintaining 826.3 mAh g⁻¹ even at a high rate of 2C. When the rate was reverted to 0.2C, the specific capacity reached an impressive value of 990.2 mAh g⁻¹. These findings underscore that crystal facet engineering is an effective method for optimizing catalyst performance. This research not only enhances the comprehension of surface structure-driven electrocatalysis in LiS chemistry but also paves the way for the practical application of natural hematite in advanced energy storage systems.