Search papers, labs, and topics across Lattice.
This study introduces a thermodynamic theory that links the Stern-layer capacitance of electric double layers to the local solvent composition in binary liquid mixtures, revealing a negative contribution to the inverse differential capacitance. The findings indicate that the surface potential can exhibit nonmonotonic behavior with respect to surface charge density, leading to a first-order transition between distinct electric-double-layer states. By applying a common-tangent construction to derive phase diagrams and validating the theory against experimental data for tetrabutylammonium chloride in water/1-propanol mixtures, the authors demonstrate the significant impact of solvent composition on capacitance and interfacial phase behavior.
Surface potential can become nonmonotonic with charge density, leading to unexpected first-order transitions in electric double layers.
We develop a thermodynamic theory of electric double layers in binary liquid mixtures by allowing the Stern-layer capacitance to depend on the local solvent composition. This coupling produces an additional negative contribution to the inverse differential capacitance. As a result, the surface potential can become a nonmonotonic function of the surface charge density, leading to negative differential capacitance and a voltage-induced first-order transition between two electric-double-layer states. We determine the coexistence condition using a common-tangent construction for the surface-charge-controlled grand potential and obtain phase diagrams in terms of the Stern-capacitance contrast, surface charge density, bulk composition, and surface potential. We also compare the theory with capacitance data for tetrabutylammonium chloride in water/1-propanol mixtures, finding semi-quantitative agreement in the continuous-response regime. These results suggest that solvent exchange inside the Stern layer can strongly control the capacitance and interfacial phase behavior of binary mixtures.
