Understanding Li-Al-CO layered double hydroxides. (II) Interface electrochemical properties.

In the current work, the interface electrochemical (IEC) properties of Li-Al-CO layered double hydroxides (LDHs) with structural positive charges were investigated by experiments and model fitting. The surface charge densities of the LDHs at different electrolyte (NaNO) concentrations and pH were determined using acid-base titration. The effective structural charge density and the point of zero net charge are obtained to be ∼5.27 × 10 C/m and 9.22, respectively. On the basis of the general surface-charging (1-pK and 2-pK) models, the intrinsic surface reaction equilibrium constants pK, pK, and pK are obtained to be -8.50, 7.49, and 9.51, respectively. The general 2-pK model is combined with the diffuse layer model (DLM, an electrostatic model) to fit the surface-charging data. Model predictions are in good agreement with the experimental data, indicating that the general surface-charging models are reasonable and that the surface-charging behavior of Li-Al-CO LDHs can be described using the 2-pK/DLM model. To the best of our knowledge, this is the first report on the IEC properties of Li-Al LDHs, providing a better understanding for the features of Li-Al LDHs.