The prospect of having a selection of key chemical reactions directly activated by solar energy would be highly attractive from both an energy and environmental point of view.This goal might be achieved via catalysis and more specifically photocatalysis, where the
required chemical activation energy (in the presence of a catalyst) is provided by light.
In addition to being highly favorable from an energy point of view - since solar energy is
free and in practice inexhaustible – photocatalysis allows for chemical reactions which can
proceed with a positive standard free energy of reaction. Some examples are given below:
A very interesting example is the photocatalytic splitting of water into hydrogen and oxygen using solar energy which has attracted substantial interest as a source for hydrogen fuel, for example, for the use in fuel cells. The key question is how to design catalysts which can operate with a very high efficiency when driven by solar light? A titanium dioxide catalyst irradiated by ultraviolet light can, for example, accelerate the breakdown of various organic compounds. Again, it
would be highly attractive find catalysts which can be driven by solar light.