Naturally, the solid liquid interface interaction widely exists. The study of electrode and aqueous solution interface is significant to the application of capacitive deionization as the principal reaction takes place at the interface. This paper focuses on the pure oxide thin-film, TiO₂, in an aqueous solution concerning the response to solution chemistry including protons and specific adsorbing ions, phosphate for instance. Through the measurement of zeta potential and open circuit potential, the mechanism that the interfacial properties can be influenced by solution chemistry is illustrated. With the results of capacitance at different state of solution chemistry, the relationship between the interfacial properties, especially the surface potential, and the capacitance is obtained. The electrochemical capacitance is related to the surface potential of TiO₂ porous thin-film and can be changed with the addition of protons and specific adsorbing ions. The capacitance increases away from isoelectric point in absence of phosphate, and phosphate addition displays an optimal effect over the neutral range of pH from 5 to 9, where many oxides are highly stable with quite low dissolution. Based on the results above, capacitive deionization system with phosphate modified TiO₂ porous thin-film is designed, which possesses better deionization performance compared to the one without specific adsorption. It is believed that these TiO₂ porous thin-film could be used as electrodes or coatings for electrodes due to their high surface area, good wettability of the pore walls and controllable surface potential. Further study of the interface is important in the development of capacitive deionization.