Electrochemical Insertion/Deinsertion of CO ₃ ^2– into/from Layered Double Hydroxide Interlayers

The achievement of carbon neutrality requires not only reducing CO2 emissions but also developing strategies for its effective utilization. In this study, we explored the feasibility of employing carbonate ions, captured in alkaline solutions via direct air capture (DAC) based on chemical absorption, as charge carriers in electrochemical energy storage devices. Layered double hydroxides (LDHs) were selected as the host materials for CO32– storage, and the influence of their constituent metal elements on the insertion–extraction behavior of carbonate anions was systematically investigated. Cyclic voltammetry in a model electrolyte of 1 mol kg–1 K2CO3 (pH 12.1) revealed no electrochemical activity from MgAl-LDH, whereas MnAl- and NiAl-LDH exhibited redox responses associated with anion insertion–extraction. Although NiAl-LDH was expected to undergo redox reactions, these did not proceed within the potential window of the electrolyte. Comparison with HCO3– and OH– indicated that the intercalating species was predominantly CO32– anions. Galvanostatic charge–discharge measurements demonstrated that structurally optimized MnAl-LDH, with well-developed anion storage sites, delivered initial charge and discharge capacities of 288 and 248 mA h g–1, respectively. XRD and XPS analyses confirmed the reversible interlayer expansion–contraction and the Mn3+/2+ redox process accompanying CO32– insertion–deinsertion. While the capacity decreases to 90 mA h g–1 after 20 cycles, this issue may be alleviated through compositional tuning and by enhancing the oxidative decomposition resistance of the electrolyte. Electrochemical impedance spectroscopy revealed no significant difference in activation energy between CO32– and OH– insertion. Importantly, the electrochemical control of CO32– release, which is otherwise stabilized and scarcely exchangeable once incorporated into LDH interlayers, suggests promising applicability in ion-exchange processes, such as the removal of hazardous anions.