摘要
The growing dependence on lithium has intensified the need for sustainable and selective extraction strategies from complex brines. Herein, an ion-exchange membrane (IEM)-free hybrid capacitive deionization (HCDI) system with δ-MnO2–decorated MXene (MNMX) and amine-functionalized biomass-derived graphene oxide (NGO) was fabricated to serve as the pseudocapacitive cathode and anode, respectively, to selectively recover Li+ and suppress co-ion expulsion. MNMX possesses accordion-like layers and can serve as the support and intercalation sites to coat with δ-MnO2 rods with a thickness of 0.6–0.8 μm. XPS results confirm the presence of MnO2 on the MXene surface, while surface charge measurements show that MnO2 incorporation enhances the stability of the negative surface potential in the MNMX composite and the net positive surface charge of NGO is marginal at nearly neutral pH. The NGO||MNMX pair on the hybrid CDI setup delivers a specific electrosorption capacity (SEC) of 41.8–48.8 mg g−1 at 100 mM LiCl with energy consumption 0.21–0.28 Wh g−1 at 1.2 V. Notably, the system exhibited robust Li+ selectivity, achieving 2.2–9.9-fold enhancements over competing ions (Mg2+, K+, and Na+) in binary environments. The mechanism is proposed based on the strong thermodynamic preference for Li+ intercalation via reversible Mn4+/Mn3+ redox reactions in the MNMX cathode, combined with effective co-ion screening by the positively charged NGO anode. These findings present a facile, highly efficient, and scalable pathway for selective lithium recovery through HCDI.
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•δ-MnO2–MXenes with NH2–biomass-derived N-GO were fabricated for HCDI application.•The HCDI garners a superior SEC of 48.8 mg g−1 with ASAR of 5.7 mg g−1 min−1 at 50 mM LiCl.•The reversible Mn3+/Mn4+ redox sites in MnO6 octahedra enhance rapid Li+ electrosorption.•Enhanced Li+/Mg2+ selectivity of 2.2–9.9 folds over multiple ions at different Li/Mg ratios.