Category: 15. Semiconductor Electrodes and Photoelectrochemical Cells

In this section, we consider a complete photoelectrochemical (PEC) cell such as that shown in Figure 15.21. The cell consists of a photoelectrode and a metal counter electrode that are immersed in a common electrolyte. For example purposes, we assume that the photoelectrode is an n-type semiconductor, which acts as the anode in the cell.…

What happens when the illuminated electrode is at open circuit? The answer to this question is perhaps most easily seen from Equation 15.21 for an n-type semiconductor, which includes both the photocurrent and the current due to the potential-dependent majority carrier current. At open circuit, the net current is equal to zero. In an n-type…

To this point in the chapter, we have presented a brief introduction to semiconductors and have described the interface that develops when they are put into contact with an electrolyte. Current flow under dark conditions has also been described. Finally, we looked briefly at the light absorption characteristics of semiconductors. We are now ready to…

Now that we have examined the electrochemical behavior of semiconductors in the dark, the next step is to include photoelectrochemical (PEC) effects. Toward that end, this section describes the absorption of light by semiconductors. The principal mechanism for the absorption of photon energy by a semiconductor is the excitation of an electron from the valence…

The space-charge layer introduced in the previous section plays a critical role in the flow of current for a semiconductor electrode. The band diagrams that correspond to open-circuit, positive overpotential, and negative overpotential for n-type semiconductors are shown in Figure 15.13. At open circuit , the net flow of current is zero and the conduction band energy increases…

We will now examine what happens when a semiconductor is placed in an electrolyte solution. Initially, we will consider the situation at open circuit under dark conditions (i.e., no photoexcitation of electrons). We will then examine how the interface that is established influences the flow of current. Finally, we will look at the impact of…

Before going any further, we need to relate the energy scale commonly used with semiconductors to the standard hydrogen electrode (SHE) scale familiar to electrochemists and electrochemical engineers. As you know, the SHE scale uses the hydrogen electrode under standard conditions as the reference potential for all electrochemical reactions. In contrast, the most common reference…

Solid materials can be classified by their ability to conduct electrical current as metals, semiconductors, and insulators. The ability to conduct is directly related to the availability of and mobility of charge carriers (e.g., electrons). As you may recall from your basic chemistry course, electrons can only occupy discrete energy levels in atoms. Hence, you…