Constant pH solution

In this type of cell both electrodes are immersed in the same constant pH solution. An illustrative cell is [27,28] n-SrTiOs photoanode 9.5-10 M NaOH electrolyte Pt cathode. The underlying principle of this cell is production of an internal electric field at the semiconductor-electrolyte interface sufficient to efficiently separate the photogenerated electron-hole pairs. Subsequently holes and electrons are readily available for water oxidation and reduction, respectively, at the anode and cathode. The anode and cathode are commonly physically separated [31-34], but can be combined into a monolithic structure called a photochemical diode [35]. 

The development of the glass electrode, which is reversible to hydrogen ions, was a major contribution toward the development of the measurement of pH. A common glass electrode consists of a thin bulb of a special glass (made of silica and sodium and calcium oxides), responsive to hydrogen ions this construction makes the glass electrode a high impedance device. The bulb is filled with a solution of constant pH and an inner reference electrode, which is reversible to the anion in the constant pH solution, is placed in it. A common such solution is hydrochloric acid and the inner reference electrode is silver chloride. A schematic picture of the electrode is shown in Fig. 83. 

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