Behavior of 2:1 and 3:1 Electrolytes at Polarizable Interfaces

The behavior of the electrical double layer (DL) is known to be different at polarizable interfaces, specifically, at a metallic electrode (where the dielectric constant of the electrode is infinitely large, epsilon(1) -> infinity) and at an air/electrolyte interface (where the dielectric constant of the electrode is epsilon(1) = 1) than is the case for unpolarized interfaces. For the polarized interface, if multivalent ions are present, these ions are attracted/repelled more than is the case for monovalent ions. Therefore, the divalent/trivalent ions (assumed to be cations to be specific) accumulate near the metallic electrode more than for the unpolarized electrode and a charge inversion occurs. In such asymmetric electrolytes, this results in a large potential at zero electrode charge. The behavior is reversed for the air/electrolyte interface. This is more pronounced at low reduced temperatures (or, equivalently, at high ionic couplings). The anomalous capacitance behavior of the DL is seen for the unpolarized electrode, where the temperature derivative of the capacitance is positive at low reduced temperatures (characteristic of electrolytes with ions with high ionic couplings or molten salt DLs at room temperatures) while it is negative at high reduced temperatures (characteristic or aqueous solutions of monovalent salts at room temperatures). At least for the states we consider, this anomalous behavior is enhanced for the air/electrolyte interface but vanishes for a metallic electrode. Our Monte Carlo simulations of these phenomena are reported.