Organic anion-intercalation boosting intrinsic Cl⁻ capture capability of layered double hydroxide anode for enhanced capacitive deionization

Layered double hydroxides (LDH) hold great promise as capacitive deionization (CDI) anodes owing to high Cl⁻ capture capacity and abundant interlamellar ion transport channels. However, their narrow interlayer spacing results in sluggish ion diffusion and huge volume variation during Cl⁻ adsorption/desorption, which becomes worse due to large ionic radius of Cl⁻. Herein, we reveal the significant effectiveness of organic anions intercalation on boosting intrinsic Cl⁻ capture capabilities of LDH anode. Compared with traditional inorganic anions-intercalated LDH anode, organic anion-intercalated LDH possess expanded interlayer spacing and increased proportion of highly active divalent metal ions in the host layer. Theoretical calculations unveil that organic anion intercalation endows LDH with stronger Cl⁻ capture ability, faster ions diffusion behaviors, and stronger bonding strength with positively charged host layers. As expected, the prepared seven kinds of organic anion-intercalated LDH anodes all manifest fast pseudocapacitive reaction kinetics and enhanced desalination performance; particularly, sodium dodecyl sulfate (SDS) intercalated LDH (LDH-SDS) anode exhibits a large desalination capacity of 58.6 mg g⁻¹ and excellent cyclic stability (76.9% retention ratio over 300 cycles), surpassing most of previously reported LDH-based CDI anodes. A series of in-situ/ex-situ characterizations further reveal outstanding structural stability and electrochemical reversibility of LDH-SDS anode. This work demonstrates great potential of crystal modulation on improving intrinsic ions capture capability of LDH and paves new insights for developing advanced CDI electrodes.