A scalable three-dimensional porous λ-MnO2/rGO/Ca-alginate composite electroactive film with potential-responsive ion-pumping effect for selective recovery of lithium ions

Abstract

A scalable three-dimensional (3D) porous composite electroactive film consisting of λ-MnO2, reduced graphene oxide (rGO) and calcium alginate (Ca-alg) was successfully fabricated and employed for the selective extraction of Li+ ions with low concentration via an electrochemically switched ion exchange (ESIX) technology. The Li+ ion adsorption capacity of the obtained λ-MnO2/rGO/Ca-alg composite electroactive film reached as high as 32.7 mg g−1 and more than 90% of its equilibrium adsorption capacity was achieved in 1 h. The λ-MnO2/rGO/Ca-alg composite electroactive film displayed evident selectivity towards Li+ ions. The separation factors for Li+/Na+ and Li+/Mg2+ reached 1040.57 and 358.96, respectively, while tested in simulated brine. The composite film also showed superior electrochemical stability, and the normalized ion exchange capacity retained at 98.3% of its initial value even after 100 successive cycles. The excellent Li+ ion recovery performance of the obtained composite film should be attributed to its low ion transfer resistance owing to the porous network structure and the potential-responsive ion-pumping effect in the ESIX process. In addition, a large-scale of such a composite electroactive film could be effectively fabricated by controlling the spreading area of the mixed solution consisting of λ-MnO2, rGO and alginate binder. It is expected that such a scalable 3D porous composite film could be a promising alternative for the recovery of lithium ions from salt lake brine.