Phase Transformation Induced Basal Plane Capacitance Enhancement in Two-Dimensional Materials for Electro-Driven Ion Capture

The capacitive deionization (CDI) technique using two-dimensional (2D) layered Faradaic electrodes offers a promising approach to desalination, but the desalination efficiency of currently engineered electrodes remains insufficient due to unclear charge storage mechanisms. Herein, based on typical 2H and 1T phases of MoS₂, we systematically investigated the underlying structure-capacitance relationship of 2D materials at the atomic level by revealing differences in interlayer ion storage confined by molecular layers. Our study reveals that octahedrally coordinated 1T phase with a high spin state of unpaired electrons exhibits a higher pseudocapacitive ratio compared to the 2H phase because of the enhanced interfacial charge transfer polarization, reduced surface ion migration barriers, and increased interlayer ion enrichment. Furthermore, the potential molecular layer structure evolution triggers the dynamic migration of ion intercalation sites, further constraining the ion storage performance of the 2H phase. This study offers guidance for optimizing the ion storage performance of 2D materials through phase engineering.