Bifunctional Modification Enhances Lithium Extraction from Brine Using a Titanium-Based Ion Sieve Membrane Electrode

Salt lake brine has become a promising lithium resource, but it remains challenging to separate Li⁺ ions from the coexisting ions. We designed a membrane electrode having conductive and hydrophilic bifunctionality based on the H₂TiO₃ ion sieve (HTO). Reduced graphene oxide (RGO) was combined with the ion sieve to improve electrical conductivity, and tannic acid (TA) was polymerized on the surface of ion sieve to enhance hydrophilicity. These bifunctional modification at the microscopic level improved the electrochemical performance of the electrode and facilitated ion migration and adsorption. Poly(vinyl alcohol) (PVA) was used as a binder to further intensify the macroscopic hydrophilicity of the HTO/RGO-TA electrode. Lithium adsorption capacity of the modified electrode in 2 h reached 25.2 mg g^-1, more than double that of HTO (12.0 mg g^-1). The modified electrode showed excellent selectivity for Na⁺/Li⁺ and Mg²⁺/Li⁺ separation and good cycling stability. The adsorption mechanism follows ion exchange, which involves H⁺/Li⁺ exchange and Li-O bond formation in the [H] layer and [HTi₂] layer of HTO.