Mott illuminated electrode

Figure 11. Mott-Schottky plots of reciprocal square of differential capacitance of n-type TiO electrode in 0.5M HfSO, vs, electrode potential. (O) In the dark (O) under illumination as in Figure 10. Intercept at C = oo gives the value of the flat-band potential (19).

The selection of a reference potential at the Ohmic contact is arbitrary and was chosen to emphasize the degree of band bending and straightening in the semiconductor. The development of Mott-Schottky theory in Section 12.3.2 employs a potential referenced to the Ohmic contact. A difference in sign will be seen if the potential is referenced instead to a reference electrode located in the electrolyte. The potential of the electrolyte has been fovmd to be independent of current and illumination intensity when referenced to an external quantity such as the Fermi energy of an electron in vacuum. This concept has proved useful for predicting the interaction between semiconductors and a variety of redox couples. The lUPAC standard for photoelectrochemical systems, in fact, is that the potential is referred to a reference electrode in the electrolyte. ... 

Fig. 5.22 Mott-Schottky plot of the space charge capacity vs. electrode potential for p-GaAs at pH 1, in the dark and under illumination. Insert Ua, vs. limiting photocurrent. (After ref. [43])...

The three different techniques that can estimate the Ea, are illuminated OCP (Section Illuminated Open-Circuit Potential (OCP) ), Mott-Schottky (Section Mott-Schottky ) and photocurrent onset (Section Three-Electrode J-V and Photocurrent Onset ). The Eft, should be independent of the technique used to determine it. Due to the inherent shortcomings of each technique, there is often a lack of agreement of the values determined by the various analyses. Researchers should be aware of these limitations in interpreting results. 

---