Hierarchical ZIF-8@MnO₂/AC electrodes for lithium enrichment in capacitive deionization: Coupling ion sieving with redox-assisted storage
Journal
Electrochimica Acta
Journal Volume
572
Start Page
149435
ISSN
00134686
Date Issued
2026-10-01
Author(s)
Abstract
Efficient lithium (Li) enrichment in capacitive deionization (CDI) remains challenging because of the ultralow Li concentration in saline water and severe competition from coexisting ions. Herein, a proof-of-concept hierarchical ZIF-8@MnO₂/AC electrode is developed by integrating an ion-sieving ZIF-8 layer, redox-active MnO₂ domains, and a conductive porous carbon framework. The composite exhibits a specific surface area of 632 m² g⁻¹ with hierarchical micro–mesoporous channels, which contributes to improved electrochemical behavior, including a specific capacitance of 38.05 F g⁻¹ and a reduced charge-transfer resistance of 26.2 Ω compared with MnO₂/AC (118.0 Ω). In single-ion LiCl solution, the electrode achieves a salt adsorption capacity of 27.98 mg g⁻¹, exceeding those of AC (17.30 mg g⁻¹) and MnO₂/AC (24.28 mg g⁻¹). Under mixed-ion conditions, it exhibits improved Li⁺ preference, with selectivity coefficients of 3.73 (Li/Na), 6.72 (Li/K), 14.23 (Li/Mg), and 10.84 (Li/Ca). In competitive brine containing trace Li⁺, staged electrosorption–desorption over 10 cycles increases the Li fraction from 0.16% to 50.03%, corresponding to more than 300-fold enrichment in relative abundance. The electrode also shows low energy consumption ( E ₘ ≈ 0.026 kWh mol⁻¹ and E ᵥ ≈ 0.021 kWh m⁻³). These results suggest a coupled ion transport–storage mechanism, in which ZIF-8 regulates ion access, MnO₂ provides redox-assisted Li⁺ storage, and the porous carbon framework facilitates charge transport, offering insight into hierarchical electrode design for electrochemical Li enrichment.
Subjects
Capacitive deionization
Hierarchical electrode
Ion sieving
Lithium enrichment
MnO₂
Redox-assisted storage
ZIF-8
Publisher
Elsevier Ltd
Type
journal article