Photoelectrolysis occurs in a photoelectrochemical cell when light is used for electrolysis. In other words, photoelectrolysis is the conversion of light into a current, and then the division of a molecule using that current.
Photoelectrolysis' main attractiveness to many engineers and technologists is its potential to divide water into hydrogen and oxygen. (In this case, the process is sometimes known as water splitting or splitting water.) According to Crabtree, et al., achieving a hydrogen economy requires deriving hydrogen efficiently and inexpensively from natural sources without using fossil fuels.[1] Photoelectrolysis is often seen as having the potential to fulfill that need. (In contrast, steam reforming usually or always uses a fossil fuel to obtain hydrogen.) Photoelectrolysis is sometimes known colloquially as the hydrogen holy grail for its potential to yield a viable alternative to petroleum as a source of energy; such an energy source would supposedly come without the sociopolitically undesirable effects of extracting and using petroleum.
Some researchers have practiced photoelectrolysis by means of a nanoscale process. In fact, Crabtree, et al. claimed that with suitable semiconductors, nanoscale photoelectrolysis of water could someday reach greater efficiency than that of "traditional" photoelectrolysis. Semiconductors with bandgaps smaller than 1.7 electronvolts would ostensibly be required for efficient nanoscale photoelectrolysis using light from the Sun.