Contributions of water dipoles to double layer properties: A three-state water model

Differences between various two state water models in the literature are elucidated. A model is proposed which involves an equilibrium between dimers and monomers on the electrode surface. An approximate consideration of the waterwater and watermetal interactions on the surface indicates (θ_dimer/θ_monomer) {difference between}2 at 25°C. Application of the model to a calculation of the surface potential g^s(dipole) of water in the mercury-solution interface as a function of electrode-charge yields +0.03 V at the pzc. The calculated g^s(dipole) varies from +0.16 V to -0.10 V when the electrode charge is varied from +16 to-16 υC cm^-2. Evaluation of the dipole capacitance as a function of electrode charge shows a water contribution to the capacitance which would not effect the observed value, ie there would be no water-derived capacitance hump.