Principles and Limitations of Photoelectrochemical Fuel Generation

Photoelectrochemical (PEC) cells could play a pivotal role in meeting future energy demands. In PEC cells, semiconductors are used to convert solar energy directly into chemical energy, i.e. to drive thermodynamically uphill reactions to produce valuable products such as fuels. The “classic” application of PEC cells is to produce hydrogen through water splitting, although production of other chemicals is possible. In this chapter, the basics of photoelectrocatalysis are discussed. The thermodynamic requirements of the semiconductor will be touched upon first. Then, the properties of the semiconductor/electrolyte interface will be discussed, both under dark conditions and under illumination. Afterward, different PEC device configurations, device efficiencies, and limitations of the PEC devices themselves will be presented. We will also briefly touch upon PEC cells used for different applications than “classic” water splitting and the corresponding theoretical limitations. Finally, recent approaches to enhance the catalytic activity or to improve the stability of PEC cells by surface modification are described.