Chandekar developed a low-cost scalable manufacturing process to produce both the nano-structured template and the strained titanium dioxide coating. It was further found (Thulin and Guerra, 2008) that the strain also favorably shifted the band-edges to overlay the hydrogen evolution potential, and further still that the strain improved hole mobility, for lower charge recombination rate and high quantum efficiency. In 2002, Guerra (Nanoptek Corporation) discovered that high localized strain could be induced in semiconductor films formed on micro to nano-structured templates, and that this strain shifted the bandgap of the semiconductor, in the case of titanium dioxide, into the visible blue. The bands are separated by a wide band gap of at least 3 eV, so that these materials absorb only UV radiation.Ģ microstructure has also been investigated to further improve the performance. Including SrTiOģ, this kind of semiconducting titanates, the conduction band has mainly titanium 3d character and the valence band oxygen 2p character. In 1967, Akira Fujishima discovered the Honda-Fujishima effect, (the photocatalytic properties of titanium dioxide).Ģ and other metal oxides are still most prominent catalysts for efficiency reasons. To maximize current, anode and cathode materials need to be matched together the best anode for one cathode material may not be the best for another.

Good photoanodes, on the other hand, will have early onset of the hydrogen evolution reaction in addition to high current and rapid photocurrent growth. A good photocathode will have early onset of the oxygen evolution reaction (low overpotential), a large photocurrent at saturation, and rapid growth of photocurrent upon onset. While the listed requirements can be applied generally, photoanodes and photocathodes have slightly different needs.

In addition to these requirements, materials must be low-cost and earth abundant for the widespread adoption of PEC water splitting to be feasible. stability: materials must be stable to prevent decomposition and loss of function.catalytic activity: high catalytic activity increases efficiency of the water-splitting reaction.

For example, in a water-splitting photoelectrochemical cell, the excitation, by light, of an electron in a semiconductor leaves a hole which 'draws' an electron from a neighboring water molecule: The situation within a photoelectrolytic cell, on the other hand, is quite different. The classification of photoelectrochemical cells which includes Grätzel cells meets this narrow definition, albeit the charge carriers are often excitonic. The standard photovoltaic effect, as operating in standard photovoltaic cells, involves the excitation of negative charge carriers (electrons) within a semiconductor medium, and it is negative charge carriers (free electrons) which are ultimately extracted to produce power. The second is a photoelectrolytic cell, that is, a device which uses light incident on a photosensitizer, semiconductor, or aqueous metal immersed in an electrolytic solution to directly cause a chemical reaction, for example to produce hydrogen via the electrolysis of water.īoth types of device are varieties of solar cell, in that a photoelectrochemical cell's function is to use the photoelectric effect (or, very similarly, the photovoltaic effect) to convert electromagnetic radiation (typically sunlight) either directly into electrical power, or into something which can itself be easily used to produce electrical power (hydrogen, for example, can be burned to create electrical power, see photohydrogen). The first produces electrical energy similarly to a dye-sensitized photovoltaic cell, which meets the standard definition of a photovoltaic cell. Sources of electricity or hydrogen via electrolysisĪ ' photoelectrochemical cell' is one of two distinct classes of device.

Anode cathode pic