Charge transfer cocrystal hydrogels for solar-driven lithium extraction and water co-generation

Abstract

Lithium is a vital strategic resource for the modern energy transition. However, conventional adsorption methods are limited by slow extraction kinetics and substantial freshwater consumption. In this work, a lithium-extracting hydrogel (LEH) driven by a novel charge-transfer (CT) organic cocrystal (ATQ) is developed for interfacial solar evaporation-driven lithium extraction. ATQ cocrystals exhibit strong CT interactions, panchromatic absorption, and a high photothermal conversion efficiency of 90.27 ± 0.85 % at 1550 nm, efficiently harnessing the energy within the near-infrared II (NIR-II) region of the solar spectrum. The LEH hydrogel is optimized through structure design, achieving an evaporation rate of 2.48 kg m⁻² h⁻¹. Evaporative flow-driven convection suppresses the concentration polarization of protonated lithium titanate (HTO) and accelerates ion transport. Localized interfacial heating enhances adsorption kinetics, enabling efficient lithium extraction. The LEH demonstrates a Li⁺ adsorption capacity of 23.4 mg g⁻¹ in simulated solution under 1 Sun and exhibits superior Li⁺/Mg²⁺ selectivity with a separation factor of approximately 180 in high-magnesium brines. Importantly, the collected condensate can be reused as the water source for preparing acidic eluent for Li⁺ stripping, enabling condensate-assisted regeneration of the LEH. This integrated strategy highlights the potential of coupling solar-driven lithium extraction with freshwater co-generation to reduce freshwater demand in salt lake lithium recovery.