Layer at the Insulator-Solution Interface

The double layer at the insulator-solution interface is related to the semiconductor solution interface. The difference between a semiconductor and insulator is rather conditional. Like the semiconductor, the insulator has a forbidden energy gap between the valence band and the conduction band, but the gap is much larger compared to that in the semiconductor. But unlike the semiconductor, the insulator is characterized by a small conductivity in comparison with semiconductors such as Si, Ge, etc. 

FIGURE 19. (a) Chemiosmotic model of phosphorylation, (b) Electrodic model of phosphorylation. 

a feature of the insulating electrode is the deep electric field penetration into the electrode. By solving the Poisson equation for the 

FIGURE 20. The band bending (a), distribution of the charge (b), and potential (c) at the insulator-electrolyte interface. 

Debye length may reach several centimeters. But, in reality, the traps in the insulator reduce the depth of penetration of the field. One distinction of the insulating electrode from the semiconductor is the fact that the thickness of the insulating electrode may be less than the Debye length in it. It is then possible to obtain a mutual influence of the potential distribution at opposite sides of the insulating membrane. 

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