Water-containing layered materials have found various applications such as water purification and energy storage. The highly structured water molecules around ions under the confinement between the layers determine the ion storage ability. Yet, the relationship between the configuration of interlayer ions and water structure in high ion storage layered materials is elusive. Herein, using layered double hydroxides, we demonstrate that the water structure is sensitive to the filling density of ions in the interlayer space and governs the ion storage. For ion storage of dilute nitrate ions, a 24% decrease in the filling density increases the nitrate storage capacity by 300%. Quartz crystal microbalance with dissipation monitoring studies, combined with multimodal ex situ experiments and theoretical calculations, reveal that the decreasing filling density effectively facilitates the 2D hydrogen-bond networking structure in water around interlayer nitrate ions along with minimal change in the layered structure, leading to the high storage capacity.

In layered materials, the layer-stacking sequence allows the tuning of ion transport and storage properties by modulating the host–ion interactions. However, unlike in the case of cations, the relationship between the stacking sequence and anion transport and storage properties is less clearly understood. Herein, we demonstrate that the stacking sequence governs the nitrate-storage properties of layered double hydroxides (LDHs); the 2H 1 polytype enhances the nitrate-storage capacity to 400% of that of the 3R 1 polytype. A quartz crystal microbalance with dissipation monitoring combined with multimodal ex situ experiments indicated that the high ion-storage capacity of the 2H 1 polytype originates from the soft nature of LDHs lattices, which facilitates nitrate with minimal lattice changes. In contrast, the rigid lattice of the 3R 1 sequence requires a notably large lattice expansion, which is detrimental to ion storage. Our findings can aid the rational design of anion-host interaction-derived functionalities.