Absolute energy scale showing the redox Fermi levels of several redox couples. The figure also shows the positions of the conduction and valence bands of CdS, Fe₂O₃ and TiO₂ in electrolytes with pH values equal for their respective pH_pzc values: CdS – pH 2.0; Fe₂O₃ – pH 8.60. TiO₂ – pH 4.30.¹⁵  At these pH values, the surface dipole associated with ionic states on the surface is assumed to be close to zero. Note that the band energies of the oxides are shifted upwards by increases in pH and downwards by decreases in pH.