The influence of surface potential on quantities measuring for metal oxide/electrolyte solution interface: theoretical study based on 1-pK and 2-pK surface charging models

Two models of oxide surface charging, 1-pK and 2-pK, and the basic Stern model of electric double layer were applied in order to calculate surface potential. The potential was calculated by means of exact equations developed for these models, simplified equations, which neglected electrolyte ion adsorption, and the Nernst equation. The potentials obtained in this way were used to calculate: surface charge, electrokinetic potential, isotherms of electrolyte ion adsorption, temperature dependence of surface potential, and the molar heat of proton adsorption. The calculated values were compared with experimental data for the system gamma-Al2O3/NaCl. It was found that, except for surface charge, the calculated quantities were very sensitive to the surface potential. The best results were obtained when this potential was calculated by means of exact equations taking into account electrolyte ion adsorption. The analysis presented shows clearly that evaluation of the theoretical models on the basis of only one kind of experimental data is questionable. However, it is common practice.